Landscape and Urban Planning 99 (2011) 226–238 Contents lists available at ScienceDirect Landscape and Urban Planning journal homepage: www.elsevier.com/locate/landurbplan Landscape metrics in the analysis of urban land use patterns: A case study in a Spanish metropolitan area Francisco Aguilera a,∗ , Luis M. Valenzuela a , André Botequilha-Leitão b a b Environmental Planning Laboratory (LABPLAM), University of Granada, Campus de Fuente Nueva, Edificio Politécnico s/n, 18071 Granada, Spain Research Centre for Landscape, Territory and Urbanism (CIPTU), University of Algarve, Faro, Portugal a r t i c l e i n f o Article history: Received 26 April 2010 Received in revised form 4 October 2010 Accepted 19 October 2010 Available online 14 December 2010 Keywords: Spatial metrics analysis Urban land use patterns Future scenarios Cellular automata Metropolitan Area of Granada a b s t r a c t Urban growth patterns are characteristic of spatial changes that take place in metropolitan areas (MA). They are particularly prominent in more recently formed MAs, such as those in certain locations in Spain, where the structure of the traditional city has undergone sweeping changes. Given the capacity of spatial metrics to characterize landscape structure, these metrics can be a valuable instrument to identify growth patterns in MAs and to evaluate possible urban growth options, based on spatial characteristics. This article focuses on a medium-sized MA (Granada, Spain), and explores the use of spatial metrics to quantify changes in the urban growth patterns reflected in three future scenarios (2020). The scenarios were simulated with a model based on cellular automata, which reproduced three urban growth processes (aggregation, compaction, and dispersion) and four urban growth patterns (aggregated, linear, leapfrogging, and nodal). The scenarios were evaluated with metrics that quantified changes in the spatial characteristics of urban processes. Thus, for example, the NP and AREA MN allowed us to characterize the decreased aggregation of high-density residential land uses in one scenario (S1) and the linear growth patterns in industrial land uses in another scenario (S2). In this way, spatial metrics were found to be useful for the evaluation of urban planning. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Urbanization is a worldwide phenomenon that has increased significantly in the last century. According to Seto and Fragkias (2005), currently, half of the world’s population resides in urban areas, and this percentage will continue to rise. Urbanization is the most dramatic form of irreversible land transformation (Luck and Wu, 2002), affecting both landscapes as well the people who live in and around cities. Urban sprawl is a type of urban growth characterized by a low-density, dispersed spatial pattern with both environmental and social impacts. It is currently one of the main challenges for spatial planners in the 21st century (Muñiz et al., 2008; Poelmans and Van Rompaey, 2009). In Spain, urban growth has soared in recent years (Observatorio de la Sostenibilidad en España, 2006). More specifically, 1995–2007 was a period of intense economic activity that witnessed the expansion and consolidation of large metropolitan areas (i.e. Madrid, Barcelona, and Seville). During this same period, medium-sized metropolitan areas such as Malaga, Granada, and Alicante also emerged (Ministerio de Vivienda, 2006). This led to the appearance of new patterns of urban growth, which were considerably ∗ Corresponding author. Tel.: +34 958 24 04 47; fax: +34 958 24 89 90. E-mail addresses: franab@ugr.es (F. Aguilera), lvmontes@ugr.es (L.M. Valenzuela), aleitao@ualg.pt (A. Botequilha-Leitão). 0169-2046/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.landurbplan.2010.10.004 more dispersed (Muñiz et al., 2008). These processes resulted in the fragmentation and occupation of the rural landscape (EEA, 2006), an increase in population mobility and associated infrastructures (Newman and Kenworthy, 1999), and also the expansion of the urban structure of these metropolitan areas (Dematteis, 1998). A major concern in spatial planning in the Iberian Peninsula is the study of the spatial characteristics of urban processes, such as urban sprawl (Botequilha-Leitão, 2001; Ministerio de Vivienda, 2006; Dalda et al., 2006). This is also true in Europe (Antrop, 2000 Galster et al., 2001; EEA, 2006; Kasanko et al., 2006; Petrov et al., 2009) as well as in the United States (Alberti, 1999; Torrens and Alberti, 2000; Song and Knaap, 2004). Landscape ecology focuses on the analysis of landscape structure, the spatial implications of ecological processes in these landscapes and the changes that occur in them (Forman and Godron, 1986; Forman, 1995; Botequilha-Leitão et al., 2006; DiBari, 2007). Because of their evident spatial dimension, landscape ecology and spatial planning converge in a common workspace (Antrop, 2001). Consequently, landscape ecology has been increasingly employed in spatial planning (Freemark et al., 1996; Bettini et al., 2001; Botequilha-Leitão and Ahern, 2002; Steinitz et al., 2003; Corry and Nassauer, 2005; Botequilha-Leitão et al., 2006; Kim and Ellis, 2009). In fact, in the last 10 years, it has been increasingly used to study the spatial characteristics of urban processes (Herold et al., 2003, 2005; Berling-Wolf and Wu, 2004, inter alia), namely the spa- F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 227 Fig. 1. Allocation of the study area: the region of Andalusia (A); the Province of Granada (B); the Metropolitan Area of Granada (C). tial characteristics of urban patches, including their size, shape, and spatial distribution. Many spatial landscape properties can be quantified by using a set of metrics (McGarigal et al., 2002; Li and Wu, 2004; Uuemaa et al., 2009). Herold et al. (2003, 2005) and Seto and Fragkias (2005) inter alia, use the term spatial metrics to more clearly differentiate these metrics from landscape metrics. Spatial metrics characterize urban form as such (Herold et al., 2003), whereas in ecological landscape studies, landscape metrics are explicitly linked to ecological functions (Gustafson, 1998; Luck and Wu, 2002; DiBari, 2007). In this context, spatial metrics can be a very valuable tool for planners who need to better understand and more accurately characterize urban processes and their consequences (Herold et al., 2005; DiBari, 2007; Kim and Ellis, 2009). Relevant examples include the following: (i) the replacement of traditional urbanization and growth patterns typical of the Mediterranean city with other more global patterns (Dematteis, 1998); (ii) modifications in the life style of the population and an increased automobile dependence (Newman and Kenworthy, 1999); (ii) changes in the periurban landscape (Antrop, 2000); (iii) the evaluation of future planning scenarios (Van Beusekom, 2003; Franco et al., 2005); (iv) the validation and optimization of the results of simulation models (Berling-Wolf and Wu, 2004; Li et al., 2008). Aguilera (2008) reviews a large body of research focusing on the analysis of the spatial characteristics of metropolitan growth (Geoghegan et al., 1997; Alberti and Waddell, 2000; Berling-Wolf and Wu, 2004; Alberti and Marzluff, 2004; Herold et al., 2005; Li et al., 2008), and highlights the value of spatial metrics in the study of urban landscapes. According to Seto and Fragkias (2005) most of these studies focus on cities in the USA. Thus there is clearly a need to explore the application of spatial metrics to European cities. This is particularly true for Mediterranean cities because of their unique morphological characteristics and because of the changes that they are experiencing in the last years (Dematteis, 1998). Within this context, our research hypothesis is that spatial metrics are useful for territorial planning, particularly for the quantification of the spatial characteristics of urban growth in metropolitan areas in southern Europe. For this purpose, we simulated three explorative scenarios (Borjerson et al., 2006) for the Metropolitan Area of Granada (Spain) from the year 2004. Each scenario reflects the potential evolution of urban growth in 2020, based on the growth in 1985–2000, analyzed in previous work. Our study uses spatial metrics to quantify spatial processes of urban growth for each scenario. These metrics allowed us to determine the spatial characteristics and patterns generated by the simulated urban processes. Accordingly, Section 2 of this article describes the Metropolitan Area of Granada (MAG) (2.1), the cartography of land occupation in 2004 (2.2), the design (2.3) and simulation of scenarios (2.4), selected spatial metrics (2.5), the spatial characteristics of urban growth processes (2.6), and the urban occupation patterns identified with the metrics (2.7). Section 3 presents the results of the identification of occupation patterns in the three future scenarios. Finally, Section 4 discusses the results obtained, and Section 5 gives the conclusions derived from the study. 228 F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 Fig. 2. Map of land use categories in the Metropolitan Area of Granada (MAG). 2. Data and methods 2.2. Urban land use maps for the Metropolitan Area of Granada 2.1. Study area For our study, we generated a map of urban land uses, which was based on the photo-interpretation of existing aerial orthophotographs on a scale of 1:10,000 for the region of Andalusia, published by the Cartographic Institute of Andalusia in 2004. This interpretation process and subsequent digitization allowed us to create a map (Fig. 2) classified in terms of the four general categories of urban land use described below (Fig. 3). Fig. 2 also includes the main public road systems as well as the principal water courses. The rest of the non-urban areas (farmlands, forests, etc.) are all classified in the category of “matrix”. This map was rasterized with a cell size of 50 m × 50 m in consonance with the size of the Minimum Mappable Unit (MMU). The Metropolitan Area of Granada (MAG) (Fig. 1) with a surface area of 859.34 km2 has 32 municipalities (Consejería de Obras Públicas, 1999). With a population of over 500,000 inhabitants in 2009, it is regarded as a medium-sized metropolitan area in comparison to other cities in Spain (such as Madrid or Barcelona) (Feria, 2004). In the last 20 years, Granada has experienced a series of transformations that have directly affected urban land use (Aguilera, 2008). The rural landscape surrounding Granada has a very high landscape value (Menor, 2000). However, it is currently experiencing a significant transformation process that has led to the formation of the current metropolitan area. In this context, a metropolitan land use plan was published in 1999, namely, the Territorial Plan for the MAG (POTAUG) (Consejería de Obras Públicas y Transportes, 1999). However there is neither a specific institutional body at a metropolitan level nor adequate management instruments. As a result, the POTAUG lacks of regulation capacity with a series of consequences briefly described below. The transformation of the MAG is primarily the result of the expansion of rural population nuclei and the increase of urban sprawl. The resulting fragmentation and isolation of farmlands has modified the traditional agricultural system. In a parallel way, this transformation has significantly changed the mobility habits of the population and increased automobile dependence (Consejería de Obras Públicas y Transportes, 1999; Menor, 2000). Additionally, the POTAUG has not been able to prevent the abandonment and loss of productive farmland, because of urban occupation. For this reason, the agricultural sector is facing a very uncertain future. There is thus the evident need to explore potential patterns of the evolution of urban growth and their spatial characteristics. 2.2.1. High density residential In these areas, there is a predominance of residential housing structures which is typical of compact cities in southern Europe. These buildings are mostly found in the city center though there are new housing developments in urban nuclei in the metropolitan ring. This type of area has a density of circa 70 households per hectare (h/ha). The city center of Granada is a good example of this category (see Fig. 3A). 2.2.2. Low-density residential These areas are characterized by single-family houses, which are either traditional village houses (e.g. Santa Fé) or new housing developments (e.g. Monte Luz, see Fig. 3B). This type of area has a density of circa 25 (h/ha). 2.2.3. Industrial These areas include not only industrial complexes per se, but also logistics centers, i.e. storage warehouses and distribution facilities (e.g. industrial areas in Road N-323, see Fig. 3C). They are F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 229 Fig. 3. (A–D) General categories of urban land use in the MAG. generally found on the outskirts of the city, and are located at main highway intersections in the metropolitan area. 2.2.4. Commercial These areas are where large shopping centers and recreational areas are located (Armilla node, see Fig. 3D). They are usually found in the vicinity of important nodes of the metropolitan road network. 2.3. Design of future scenarios Based on the data pertaining to land occupation in the MAG in 2004 and in line with previous research (Aguilera, 2006, 2008; Valenzuela et al., 2008), we created three external explorative scenarios (Dreborg, 2004; Borjerson et al., 2006), for 2020. These scenarios were based on different shapes and patterns of urban growth in the MAG over the last 30 years. These shapes and patterns were combined in scenarios with a view to exploring the possible future evolution of this metropolitan area. It should be underlined, however, that the selected type of scenarios are not more or less accurate predictions of the future (Berdoulay, 2009), but rather different evolution possibilities of the metropolitan area. The three scenarios are: (S1) residential intense development; (S2) industrial and commercial specialization; (S3) compact development. Each scenario emphasizes one of the most important growth tendencies for this area: dispersed residential growth, compact growth of the traditional city, industrial and commercial developments, etc. Moreover, each shows different urban growth intensities, compared with the growth rate in 1985–2000 (80 ha/year). This includes lower growth rates (S3), higher growth rates (S1), and a growth rate equal to that of recent years (S2). This calculation was based on the variation of certain urban growth drivers for the study area, such as economic context and the regulation capacity of the territorial plan. (S1) Residential intense development. This scenario depicts the potential intensification of urban growth caused by increased economic activity. The result is the development of new residential areas stemming from a metropolitan plan that has a weak regulation capacity. It shows an increase of 30% in the annual growth rate recorded in 1985–2000, particularly in regard to residential land use. It is characterized by an increase of urban sprawl in residential areas. In a parallel way, industrial areas also tend to develop in the neighborhood of existing industrial areas. Commercial land use experiences a similar increase. Finally, we also included new road networks in project, since they will eventually affect growth patterns in this scenario. (S2) Industrial and commercial specialization. This scenario explores a stabilization of the economic activity registered between 1985 and 2000, and specifically directed at the creation of new industrial and commercial activity that will be enhanced in metropolitan land use plans. It is characterized by a growth rate similar to that of previous years, a significant increase in new technological/commercial/industrial areas in the vicinity of major thoroughfares, and a slight increase in residential housing developments. In this scenario, technology parks and commercial areas become new centers of attraction for high-density residential zones that are farther away from the MAG core area. Low-density residential zones continue to become more aggregated. In the same ways as S1, we also included new road network projects in this scenario. (S3) Compact development. This scenario presupposes a lesser favorable economic context but favors the development of new industrial and commercial areas. It also contemplates a more restrictive metropolitan land use plan, especially in relation to residential growth. This reflects a decrease in urban land use growth rate (−30%), particularly affecting low-density residential areas. It also means that commercial and industrial land uses tend to flourish in the areas surrounding road network nodes that provide greater accessibility. New road network projects were not included because in our opinion, they are not relevant to this type of urban development. 230 F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 residential, commercial or industrial) in that specific cell. This transition potential was obtained by combining four parameters, which were all transformed on a scale from 0 to 1. Neighborhood (N): This parameter estimates the probability of change for each cell in the raster input layer, depending on existing neighboring urban land uses and the distance to the central cell. Based on the review by Santé et al. (2010), we defined a neighborhood formed by a square window of 11 × 11 grid cells of a total of 121, i.e. 550 m by 550 m. Each of the 121 cells in the neighborhood exerts over the central cell an effect or attraction or repulsion for different urban uses. This effect depends on the type of urban land use existent in each of the neighboring cells. For example, industrial uses generally repel residential uses. Additionally, the closer to the central cell they are, the higher the repulsion effect. These attraction or repulsion values should be calculated for the study area by trial and error (White et al., 1997). A cell with the highest value is assigned with 1, and those with the lowest are assigned with 0. The other intermediate values are linearly transformed to a value between 0 a 1. Suitability (S) is composed of two raster layers: slope map and urbanizable areas. The slope map was derived from the Digital Elevation Model for the area, and was transformed by a linear transformation in values ranging from 0 to 1 with maximum values for the zones of minimum slope. The map of urbanizable areas was obtained from the areas classified as urbanizable in the metropolitan land use plan (POTAUG). Urbanizable areas received a value of 1 and non-urbanizable areas, a value of 0. Accessibility (A): This parameter is defined as the nearest Euclidian distance to the road network. Areas contiguous to the road network have a value of 1, and those farther away have a value of 0. For the rest, a linear transformation function is used. Stochastic (V): The objective of this parameter is to incorporate a randomness component that is typical of urban spatial processes (Batty and Xie, 1997). It is obtained with Eq. (1): V = 1 + (− ln(rand)) ˛ (1) where rand is a random number between 0 and 1, and ˛ is a parameter that permits an adjustment of the degree of perturbation (dispersion). The value of ˛ (0.3) was computed, based on the radial dimension (Barredo et al., 2003) and validated to better simulate the urban growth patterns identified for the MAG between 1985 and 2000. The transition potential for each urban use (Pj ) was finally obtained by combining these parameters with Eq. (2): Pj = Nj × Sj × Aj × Vj Fig. 4. Simulations (S1–S3) generated for future scenarios in the year 2020 to be evaluated with spatial metrics (Aguilera, 2008). 2.4. Simulation of future scenarios with a model based on cellular automata Based on the rules described in Section 2.3, we simulated the three types of scenario with a model based on cellular automata (CA) (Fig. 4 ). This model was developed and implemented with IDRISI Andes software (Clark Labs, 2003). It is based on theoretical premises proposed by White et al. (1997), which are the basis for other simulation models (Barredo et al., 2003; Petrov et al., 2009). To calculate the localization of urban growth areas (the quantity of simulated urban growth should be established by the user), the model employs an urban land use map (Fig. 2 in raster format as input data). For each cell in the input layer, the model obtains a transition potential (P) that represents the possibility of the appearance of a new urban land use (high-density residential, low-density (2) This model has been previously used for the simulation of the dynamics of past urban growth, more specifically for 1985–2000 (Valenzuela et al., 2008). This necessarily entailed a calibration process, especially of the attraction–repulsion values used to calculate the neighborhood. The results of the simulations were compared to 2000 urban land use map using a cross tabulation which originated an overall kappa of 0.74 (Aguilera, 2006; Valenzuela et al., 2008). However, for the simulation of the three scenarios, the parameters of the model had to be modified, especially the neighborhood parameter and its rules of attraction and repulsion. However, as shown in Table 1, other parameters were also modified. The objective was to simulate the spatial processes described for each parameter in Section 2.3. The knowledge extracted from the simulation of past dynamics (1985–2000) described above was critical to simulate the future scenarios. 2.5. Set of spatial metrics For the evaluation of the changes in land use patterns in the three simulated scenarios, a small set of spatial metrics was selected. F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 231 Table 1 Implementation of rules for scenarios in the parameters of the CA-based model. The suitability parameter remained constant in all three scenarios. Scenarios Adaptation of the rules for scenarios in the parameters of the CA-based model Residential intense development (S1) Neighborhood: The attraction strength of residential land uses for more residential land uses diminishes. Beyond a certain distance, this force is transformed into repulsion, which favors urban dispersion. Accessibility: High-capacity public highway projects are included. Stochastic parameter: The weight of the randomness factor (˛) is increased for residential land uses in order to reflect new dispersed urban growth in areas at a distance from existing urban zones. Industrial and commercial specialization (S2) Neighborhood: There is an increase in the attraction strength of public roadways on commercial and industrial land uses. The attraction strength of residential land uses on themselves also increases, which favors aggregation. Accessibility: High-capacity public highway projects are included. Their weight increases for industrial and commercial land uses. Stochastic parameter: The stochastic parameter here is similar to urban growth simulations of the past. Compact development (S3) Neighborhood: The attraction strength of residential land uses for more residential land uses increases, which favors aggregation. The attraction strength of the nodes increases industrial and commercial land uses. Accessibility: High-capacity public highway projects are not included. Stochastic parameter: The stochastic parameter is reduced to show a less dispersed growth, especially in residential land uses. Since our objective was to estimate the spatial characteristics of the different urban land uses as a whole, the metrics were computed at the class level (McGarigal et al., 2002), such that a single value was obtained for each of the various classes of urban land uses. It was rather difficult to select a reduced set of metrics since there is a wide range of metrics to choose from (O’Neill et al., 1988; BotequilhaLeitão and Ahern, 2002; McGarigal et al., 2002; Botequilha-Leitão et al., 2006; DiBari, 2007). In fact, many of them were interrelated since they are derived from the same primary measurements of the patches (area, patch number, edges, etc.) (Riitters et al., 1995). Additionally, the selection of metrics invariably depends on the objectives of the research. For this purpose, we chose six metrics (Table 2), based on the core set of 10 metrics proposed by Botequilha-Leitão et al. (2006) (for a full description of these metrics, see McGarigal et al., 2002; for a description of their application in spatial planning, see Botequilha-Leitão et al., 2006). This core set was specifically selected to support spatial planning processes. Thus, it was found appropriate to use the subset of those metrics in our research. It is our assertion that these metrics can successfully characterize various spatial processes affecting urban land uses (see following sections). 2.6. Urban spatial processes The three urban spatial processes identified in the MAG are described below. 2.6.1. Aggregation Aggregation corresponds to the clustering of patches to form patches of a larger size. This evidently reduces the total number of patches (NP), thus producing an increase in their mean area (AREA MN). The aggregation process was estimated by means of a joint interpretation of the evolution of the NP and AREA MN values, along with the PLAND, all of which have been used in a wide range of research studies (e.g. Mateucci and Silva, 2005). 2.6.2. Compaction Compaction involves the formation of rounded patches in a circular shape that makes them more compact. The inverse process is Table 2 Selected set of metrics for the analysis of urban growth patterns. The selected set of metrics is in consonance with the definition of McGarigal et al. (2002). See also Botequilha-Leitão et al. (2006) for a discussion on metrics applications and planning. Spatial metric Abrrev. Description Formulae Percent of landscape PLAND Measures the percent of the landscape PLAND = Pi = Number of Patches NP Identifies the number of patches in each of the urban land uses NP = ni Mean patch size AREA MN Calculates the average mean surface of patches AREA MN = Mean radius of gyration GYRATE MN Mean of the GYRATE. GYRATE equals the mean distance (m) between each cell in the patch and the patch centroid MGYRATE = n aij j=1 A n × 100 Pi = proportion of the landscape occupied by patch type (class) i; aij = area (m2 ) of patch ij; A = total landscape area (m2 ) ni = number of patches in the landscape of patch type (class) i hij j=1 ni z h ijr hijr = distance (m) between cell ijr [located within patch ij] and the centroid of patch ij (the average location), based on cell center-to-cell center distance; z = number of cells in patch ij z r=1 n Mean shape index SHAPE MN Measures the ratio between the perimeter of a patch and the perimeter of the simplest patch in the same area SHAPE MN = Mean Euclidean distance neighbor ENN MN Measures average distance between two patches in a landscape ENN MN = j=1 pij / min pij ni n j=1 ni hij pij = perimeter of patch ij in terms of number of cell surfaces; Min pij = minimum perimeter of patch ij in terms of number of cell surfaces hij = distance (m) from patch ij to nearest neighboring patch of the same type (class), based on patch edge-to-edge distance, computed from cell center to cell center 232 F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 Fig. 5. Land use patterns in the industrial and commercial specialization scenario (S2) as compared to the situation in 2004 for (A) industrial; (B) high-density residential; (C) commercial. Arrows 1 and 2 show industrial uses in 2004; arrows 3 and 4 depict the linear growth process in the simulated scenario; arrows 5 and 6 show high density residential for 2004; and arrows 7, 8 and 9 show the simulated growths. Finally, arrows 10 and 11 show new commercial areas around the road network nodes in the simulated scenario. elongation, in which the shape of the patches becomes more elongated. This process is measured with SHAPE MN and GYRATE MN. Lower metric values are indicative of compaction, whereas higher metric values indicate elongation. 2.6.3. Dispersion/isolation This process involves an increase in the distance that separates patches of the same land use type. It is measured by ENN MN, such that an increase reflects greater isolation. However, in contrast to classic landscape ecology studies, in the analysis of urban processes, greater isolation indicates greater dispersion. The reason for this lies in the fact that when new patches appear within existent patches, e.g. due to urban sprawl, the distance separating them decreases (see Fig. 5C, Section 3.2, for examples of the study area). Nevertheless, other spatial metrics could have been selected to measure the three previously described spatial processes. For example, the Mean Proximity Index could have been used to estimate the dispersion process. However, its dependence on the patch size and the need to establish a neighborhood radius was the reason why we decided against using it. Another possibility would have been to use only one metric for the characterization of the compaction process. However, the lower sensitivity of the SHAPE MN and the dependence on patch size of the GYRATE MN were factors that led to our decision to use both metrics instead of only one. 2.7. Urban growth patterns We established relationships between these spatial characteristics and processes described above and distinct urban growth patterns. These patterns were characterized in terms of form as well as type of land use (Galster et al., 2001; Song and Knaap, 2004). Based on the characteristics of urban land use found in European metropolitan areas (Font, 2004; Indovina, 2005), we defined four urban patterns. Aggregated pattern: This pattern corresponds to the conventional type of urban growth in Mediterranean cities: new urban areas are added onto an already consolidated city (Dematteis, 1998; Indovina, 2005). It is characterized by increased aggregation and generally by reduced dispersion. This urban growth pattern tends either to remain constant or to decrease landscape fragmentation. Linear pattern: This pattern refers to urban growth around road networks, preferably industrial or mixed industrial land use (Font, 2004). In this type of pattern we were able to identify two main processes: (i) increased or stable aggregation; (ii) decreased compaction. Leapfrogging: This pattern reflects the appearance of urban patches with a principally residential function. It is characterized by a predominance of low-density dispersed single-family houses, and is dominated by the following processes: (i) decreased aggregation; (ii) decreased elongation because of the formation of more or less rounded patches; (iii) increased dispersion. Nodal pattern: This pattern largely reflects existing industrial and commercial urban growth near the main transportation nodes. It behaves in much the same way as the urbanization pattern (decreased aggregation along with increased dispersion and compaction). However, it mainly affects industrial and commercial uses. Table 3 shows the relation between the four patterns identified and the spatial processes determined by the metrics (aggregation, compaction, and dispersion). For example, urban growth in the aggregated pattern shows greater aggregation and compaction. In contrast, the leapfrogging growth pattern reflects less aggregation and a greater dispersion of urban uses, whereas linear patterns show lower compaction values. PLAND values are not included in F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 233 Table 3 Interpretation of the three spatial processes and change in the spatial metrics values in relation to four different patterns of urban growth identified for the MAG. Spatial processes: Aggregation (Aggre), Compaction (Comp) and Dispersion/Isolation (Disp): “+” Increase, “−” Decrease. Metric values – “↑” Increase, “↓” Decrease, ( ) Possible increase/decrease. Spatial metrics Four urban patterns and three spatial processes associated Aggregative Aggre − NP AREA MN GYRATE MN SHAPE MN ENN MN Linear Comp =/− Disp =/− ↓ ↑ Aggre =/− Leapfrogging Comp −− Disp =/− Aggre − Comp − Disp + ↑ (↓) ↑ ↑ ↑ =/↓ =/↓ Nodal =/↓ this table because they are not directly related to any pattern, but rather are jointly interpreted with the rest of the metrics. 3. Results After calculating the metric values for the three future scenarios, we were able to trace the evolution of the metrics for each urban land use category with respect to their value in 2004. The changes in the metrics reflected the modification in each land use pattern in terms of its aggregation, compaction and dispersion. Table 4 shows the changes in each land use in terms of the metrics values and the related processes that were identified. The following sections provide an interpretation of the results for each scenario. 3.1. Residential intense development scenario (S1) The S1 scenario reflects relevant changes in patterns of urban land use (Table 4). Regarding industrial and commercial uses, there was significant growth (PLAND + 54% and 90%, respectively). These land uses have a more aggregative pattern, resulting from a stronger aggregation process (−11% NP and +74 AREA MN for industrial areas; stability in NP and +91% in AREA MN for commercial areas), due to the clustering of patches in their neighborhood. Residential land uses with moderate or significant growth (+21% in PLAND for low-density and +65% for high-density) exhibit a totally different behavior. High-density residential uses show increased dispersion and less aggregation as a consequence of the appearance of new patches. This is reflected in an increase in NP (+139%), and a moderate decrease in patch size (−35% AREA MN) and in mean distance to the nearest patch (−52% ENN MN). In contrast, low-density residential seems to show a more aggregative pattern, which corresponds to a larger patch size (+18% AREA MN). 3.2. Industrial and commercial specialization scenario (S2) This scenario reflects an important change in the spatial metrics, which suggests modifications in land use patterns, especially for industrial land use. The overall behavior of the metrics seems to indicate that its growth (+65% PLAND) is reflected in more elongated urban patches, which develop as follows. Some of these patches come together to form narrow ribbons along the main transportation networks. This is indicative of a tendency to linear patterns, as reflected in decreased compaction (+5% in SHAPE MN and +15% in GYRATE MN), combined with an increase in AREA MN (+26%) as a consequence of the coalescence of multiple patches forming longer ribbons (see Fig. 5A). In contrast, residential land uses also experienced slight or moderate growth (+20% in PLAND for low density residential and +10% in PLAND for high density), but their behavior was precisely the opposite. On the one hand, high-density residential land use showed a substantially lower level of aggregation (+144% in NP and −51% in AREA MN) and higher dispersion (−46% in ENN MN). Comp − Disp + ↑ (↓) (↓) (↓) ↓ Aggre + (↓) (↓) ↑ ↑ Despite this higher level of dispersion, it is worthwhile noting that their growth occurred adjacent to patches of other land uses (see Fig. 5B). On the other hand, low-density residential land use became more aggregated (+14% in AREA MN and a −4% NP). Finally the commercial land use increased the most (PLAND +332%). It showed lesser aggregation, as can be observed in the pronounced rise in the NP (+332%). There was also greater dispersion, given the reduction in the ENN MN (−43%), which reflects a much more distributed (and thus more dispersed) commercial land use throughout the territory. 3.3. Compact development scenario (S3) The S3 scenario showed the least change in land use shapes or patterns. Regarding both high- and low-density residential zones, its evident stability is reflected in the slight changes in the metrics (see Table 4). In contrast, commercial and industrial land uses showed significant growth (+113% and 26% PLAND, respectively) with a change in pattern, as can be deduced from the decreases for both land uses in ENN MN (−17% and −8%, respectively) and from the increases in NP (+117% and 7%, respectively). In the case of industrial land use, these changes were accompanied by an increase in AREA MN (+18%). Overall, these changes can be interpreted as a tendency to greater dispersion, possibly associated with an increased nodality. Fig. 6 shows how these changes originate as a consequence of the increase in the nodality of both land uses. 4. Discussion Based on the interpretation of spatial processes such as aggregation, compaction, and dispersion, we were able to use spatial metrics to identify changes in land use patterns in the three future scenarios simulated. In order to accomplish this, we based our work on the correspondence between the changes in the metrics and the spatial processes in the landscape structure (Table 3). We were thus able to satisfactorily estimate aggregation by using the NP, AREA MN and PLAND (Seto and Fragkias, 2005; Botequilha-Leitão et al., 2006), even though the applicability of other metrics to urban areas had been previously explored, such as the ENN MN (DiBari, 2007), PLAND (Alberti and Marzluff, 2004; Herold et al., 2005), and SHAPE MN Index (Mateucci and Silva, 2005). On the basis of this correspondence, we identified changes in land use patterns, supported by the spatial processes identified by the metrics (see Table 3). The scale of analysis is an aspect of particular relevance in issues pertaining to landscape ecology (Turner, 2005). In this study, the scale used was the entire metropolitan area. This identification of patterns was a simple, global way of enriching conventional analyses of land use changes (Herzog and Lausch, 2001) on a metropolitan scale. Furthermore, it provides urban planners with another instrument that they can use to evaluate different proposals 234 F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 Table 4 Interpretation of pattern changes in the different urban land uses as reflected by changes in spatial metrics values. Land use Low-density residential High-density residential Residential intense development (S1) Industrial Commercial Low-density residential High-density residential Industrial and commercial specialization (S2) Industrial Commercial Low-density residential High-density residential Compact development (S3) Industrial Commercial Metric % Change Spatial changes PLAND NP 516 AREA MN 4.51 GYRATE MN 60.39 SHAPE MN 1.25 ENN MN 200 PLAND NP 323 AREA MN 4.88 GYRATE MN 60.53 SHAPE MN 1.27 ENN MN 152 PLAND NP 354 AREA MN 4.74 GYRATE MN 58.08 SHAPE MN 1.17 ENN MN PLAND NP 18 AREA MN 4.26 GYRATE MN 64.87 SHAPE MN 1.17 ENN MN 879 +21% +3% +18% +6% +1% −5% +65% +139% −35% 22% 5% −52% +54% −11% +74% +12% Stable +4% +90% Stable +91% +22% +2% −2% Moderate increase in the land use with larger size patches (AREA MN) and a slight decrease in the ENN MN. There is a slight aggregation, as reflected in the increase in the AREA MN. PLAND NP 483 AREA MN 4.36 GYRATE MN 57.53 SHAPE MN 1.26 ENN MN PLAND NP 329 AREA MN 3.65 GYRATE MN 52.17 SHAPE MN 1.23 ENN MN PLAND NP 526 AREA MN 3.42 GYRATE MN 59.45 SHAPE MN 1.23 ENN MN PLAND NP 63 AREA MN 2.76 GYRATE MN 52.61 SHAPE MN 1.13 ENN MN 514 +20% −4% +14% −1% +1% +1% +10% +144% −51% −33% −9% −46% +66% +32% +26% +15% +5% −21% +332% +250% +26% −1% −1% −43% A moderate growth of this land use with a slight increase in aggregation, as revealed by the slight decrease in NP and the increase in AREA MN. Small low-density urban patches cluster together. PLAND NP AREA MN 3.62 GYRATE MN 54.99 SHAPE MN 1.23 ENN MN 204 +3% +8% −5% −3% −1% −3% For a small growth in residential land use (PLAND = 3%), there is a slight decrease in aggregation, which is reflected in the increase in the number of patches (+8% NP) and a slight decrease in mean patch size (−5% AREA MN). PLAND NP 136 AREA MN 7.46 GYRATE MN 77.52 SHAPE MN 1.34 ENN MN PLAND NP 428 AREA MN 3,21 GYRATE MN 55.52 SHAPE MN 1.19 ENN MN 225 PLAND NP 39 AREA MN 2.20 GYRATE MN 52.11 SHAPE MN 1.18 ENN MN Stable +1% −0.5% +1% 0% −2% +26% +7% +18% +7% +2% −8% +113% +117% −1.5% −2% +3% −17% Changes in metrics are very small (2% at the most) with only a very slight increase in this land use (PLAND). For this reason, the spatial characteristics of this use remain the same. Large increase in this land use with less aggregation, which is evidenced in the striking increase in NP and decrease in AREA MN. There is greater dispersion with the decrease in the ENN MN since it is a land use that was extremely aggregative. Important growth in industrial land use based on greater aggregation, as reflected in the increase of the AREA MN and a drop in the NP. ENN MN increases. Larger size patches are generated because of the aggregation of other existing patches. Significant growth based on greater aggregation as reflected in the increase in mean patch size while the other spatial metrics values remain stable. Slight growth of this land use with a very important growth in dispersion (very high increase in NP and significant decrease in AREA MN). Moreover, there is a drop in the ENN MN, which suggest greater dispersion. Large increase in industrial land use and all the metrics except for SHAPE MN (only a slight increase) and a decrease in the MEEN. There is greater dispersion of the land use with more elongated patch shapes. A huge increase in commercial land use (332% PLAND), combined with increases in NP and AREA MN, and a wider distribution of the land use in the territory (decrease in ENN MN). This can be interpreted as the multiple appearance of new urban patches in this land use. For a moderate growth of industrial land use (PLAND), there is a slightly higher (NP) of larger size (AREA MN). In addition, there is a wider distribution in the area of study (slight decrease in ENN MN). A significant increase in land use occupancy (PLAND), which also implies an important increase in NP and a moderate decrease in ENN MN. It reflects a greater dispersion and distribution of this land use. F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 235 Fig. 6. Nodal pattern for industrial and commercial land uses in the compact development scenario (S3). Both residential land uses patterns are not changed (arrows 3 and 4); arrows 1 and 2 show new industrial patches around the road network nodes; arrow 5 shows new commercial patches also around nodes; finally arrow 6 shows commercial patches existent in 2004. and alternatives for future developments and scenarios (Prato, 2007) in both existing and future metropolitan land use plans. Nevertheless, it should be highlighted that this general analysis could be complemented by other more detailed studies, such as those that use spatial metrics along transects or concentric rings (Luck and Wu, 2002) to better localize changes in land occupation patterns. This would make it possible to discover and locate pattern changes in the vicinity of large highway networks or in the fringe of principal urban areas. Such analyses would also permit the use of more detailed scales which could better identify small-scale dispersion processes, such as the urban growth of isolated houses, which are not detected by the adopted cell-size (50 m × 50 m). They would thus be a valid approximation that would complement a more general analysis, such as the one described in this study. Regarding the use of metrics to identify pattern changes, in certain cases, we were obliged to visually identify the maps obtained in the simulations in order to be able to classify more complex spatial behaviors. For instance, the leapfrogging pattern and the nodal pattern are not easily distinguished from each other by metrics alone. Both are characterized by relatively small patches, which are widely separated from each other. However, the nodal pattern emerges around public thoroughfare nodes, whereas the urbanization pattern can occur anywhere. Since the metrics do not have the power to discriminate these situations, visual interpretation is required. The behavior of residential and commercial land uses in the S1scenario is a clear example of this. We thus evaluated their location in the context of thoroughfare nodes in order to classify them as nodal. Equally problematic was the growth of high-density residential land uses in the S2 and S1 scenarios. Both cases showed an increase in NP, a decrease in AREA MN, and a decrease in ENN MN. A large portion of high-density residential growth was adjacent to certain urban nuclei of low-density residential (Figs. 5B and 7). Consequently, this resulted in a combined growth pattern that aggregated high-density and low-density residential zones. This made certain urban nuclei considerably denser though the high-density land use class in itself is more dispersed and fragmented (see Fig. 7). Nevertheless, other situations offered fewer doubts. This is the case of scenario S3, especially for residential uses (Fig. 8). In this scenario, the stability of the metrics corresponds to the permanence of the spatial characteristics analyzed, and thus, to the preservation of the existing land use pattern. Consequently, by combining the evaluation of metrics with a visual interpretation of spatial characteristics, we were able to characterize the changes in the urban growth patterns in future scenarios on a metropolitan scale. Regarding the results of the evaluation of pattern changes in the simulated scenarios, in scenario S3, we found that urban occupation patterns were stable. They did not produce a significant impact since urban dispersion did not increase. In contrast, there was a more pronounced transformation of urban growth patterns in the other two scenarios. In the S1 scenario, there was a more dramatic transformation of residential land uses, which are the predominant urban uses in the MAG. The S2 scenario showed a greater transformation of commercial and industrial land uses. Despite the fact that the S1 and S2 scenarios reflect a greater degree of dispersion than the S3 scenario, the S1 scenario has a more dispersed growth, due to the greater intensity of urban growth and the predominance of leapfrogging patterns, especially in residential areas. This higher dispersion can be interpreted regarding many environmental issues. For example the appearance of new urban nuclei within the rural landscape matrix results in an increase of the interface between those land uses. Potential disturbances 236 F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 Fig. 7. New high-density residential patches in residential intense development scenario (S1). New patches produce lesser fragmentation in this land use, but which correspond to aggregative growth with pre-existing residential zones. Arrow 1 shows existent high-density residential patches in 2004. Arrows 2 and 3 show new patches in the simulated scenario. Fig. 8. Stability of residential growth patterns in the compact development scenario (S3). This figure aims at depicting the stability of residential growth patterns. Arrows 1 and 2 show how the high-density residential patterns remain constant as observed in low-density residential (arrows 3 and 4); inversely arrow 5 shows unoccupied nodes in 2004 and arrow 6 the same nodes occupied by industrial uses in the simulated scenario. originates in urban areas are water pollution from source into the hydrological system, noise pollution from cars, construction and small industrial activities, habitat loss, etc. As a consequence, the disturbance introduced by S1 scenario can be assumed as a higher impact across the MAG landscape matrix. However, despite the high level of dispersion in the S1 scenario, the linear growth patterns along the main roadways that were identified in the S2 scenario (see Fig. 5A) can produce as well an extremely negative impact, sharing with S1 most of the described effects, with a special reference to the barrier effect (Forman et al., 2003; Marull and Mallarach, 2005). The result of the latter is the fragmentation of the rural landscape in the metropolitan area (Aguilera and Talavera, 2009). 5. Conclusions Spatial metrics have been used in many research studies as a valuable tool for the analysis, monitoring, and tracking of changes in land use shapes and patterns. The approaches used range from the mere description of urban landscape dynamics (Herold et al., 2003, 2005; Seto and Fragkias, 2005; Li et al., 2008) to their application as an instrument for the comparison of scenarios of urban growth (Alberti and Waddell, 2000; Berling-Wolf and Wu, 2004). The application of the spatial metrics to a metropolitan area, subject to an intense process of transformation and growth, such as in Granada (Spain) has demonstrated its usefulness for the quantification and interpretation of spatial growth characteristics and patterns in urban environments. In our study, we simulated three future scenarios that showed different spatial processes of urban growth. These processes were quantified by spatial metrics, which allowed us to measure the changes in urban occupation patterns associated with each scenario. Moreover, this quantification provided us with a simple way of evaluating the scenarios by identifying those with a greater urban dispersion (S1) or fragmentation of the adjacent rural landscape (S2), in contrast to those with a greater compaction and stability in growth patterns (S3). The results obtained illustrate the usefulness of spatial metrics for metropolitan land use planning. Spatial metrics can thus be applied to monitor changes in urban growth patterns. Furthermore, they can also be used to evaluate the spatial consequences of urban planning policies and future scenarios (Van Beusekom, 2003; Franco et al., 2005; Aguilera, 2008), based on the characterization of spatial processes, such as urban dispersion, aggregation, linear growth, and their principal environmental consequences (Galster et al., 2001; Muñiz et al., 2008). These consequences include the following: (i) automobile dependence associated with more dispersed F. Aguilera et al. / Landscape and Urban Planning 99 (2011) 226–238 growth patterns (Newman and Kenworthy, 1999); (ii) a greater consumption of land and energy associated with more dispersed growth patterns in metropolitan areas (Muñiz et al., 2008); (iii) the isolation of periurban rural spaces resulting from the decrease in the connectivity of the landscape (Marull and Mallarach, 2005; Aguilera and Talavera, 2009); (iv) impermeabilization processes in aquifer recharge zones (CWP, 1998), etc. With a view to exploring the connection between aspects related to spatial processes and their environmental and territorial consequences, analyses such as the one described in this article could be integrated in metropolitan observatories (Keiner and Arley, 2007). 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