Geography Reference
In-Depth Information
3. Methodology
We used cartographic techniques that combine remote sensing and GIS, with ecological
analysis at different spatial scales. Both methods allowed us to determine the landscape
changes and to detect pressures acting upon some areas included in the PNA during the last
decades (urban and transport infrastructures development, etc). We reviewed i) previous
studies focused on photo-interpretation techniques [30-34]; ii) land uses changes and
territorial dynamics in different environmental conditions [35-40] and iii) definition of land
uses categories [41-44]. We chose two working scales: the first analyzed the variability of the
PNA as a whole (1:50,000), and the second, that use a more detail scale, permited us to
recognize different ecological processes that occurred in the territory (1:12,500).
We used the aerial photography of Spanish Air Force of 1975 and the orthophotography of
2009 (Plan Nacional de Ortofotografía Aérea). ERDAS Imagine 9.1 software was used for
processing analogical information (1975 flight, Spanish Air Force). Previously, we had tested
ER-MAPPER and ArcGis 9.10 methods to this end. We scanned each of 150 photograms at
600 dpi. Mosaicing was conducted using Mosaic Tool extension. This tool showed the best
balanced colour result. Each photo was improved with a Root Mean Square (RMS) and its
tolerance was less than 0.5. Distortions of the photos were corrected using a Digital Terrain
Model (DTM) at 1:5,000 scale. Re-sampling method applied was the nearest neighbour
algorithm employing at least a cubic polynomial fit using 15 Control Ground Points and at
least 10% of overlapping areas. The result was a continuous image of the study area with a 5
x 5 m resolution.
Phenological changes mean different colours that depend on season and this colour difference
causes errors in the photo-interpretation so, it was necessary to balance colours for the
ortophotography of 2009 (2.5 x 2.5 m resolution).. This problem is more evident in agricultural
areas. Likewise, existing vegetation and land use maps of Madrid Region were reviewed [45,
46]. All layers were managed in a format compatible with ArcGIS 9.3 (shapefile, coverage or
GRID) referred to the WGS84 ellipsoid and UTM coordinates Zone 30 N.
The photo-interpretation considered an accuracy of the reference map unit depending on
the type of area, establishing a minimum of 0.5 ha (1:12,500 scale), similar to that used in
other studies with this orthophotography scale in forest formations [47] and of 0.61 ha
(1:50,000 scale) using cartographic techniques that merge patches (dissolve ie.) Also on the
orthophotography were required some data about the phytostructure and percentages of
canopy cover. If necessary, we worked with DGPS techniques (GPS Trimble Nomad 6GB) to
refine the patches shape.
We employed a touch screen Wacom Cintig 12WX joined to ArcGis editor. Topological
errors were processed using ARCEDIT. Finally, we assigned a topology to each layer using
ARC/INFO 9.1. Database was designed with three fields: land use, connectivity value and
surface area (ha).
The photointerpretation was completed with fieldwork. It took over 2,000 panoramic
photographs for checking on field the areas that were more complex during the
