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Data from study: Sixty-seven years of land-use change in southern Costa Rica

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posted on 19.09.2015 by Zahawi, Rakan A., Duran, Guillermo, Korman, Urs

This is the GIS data and imagery used for analyses in the article
Sixty-seven years of land-use change in southern Costa Rica by Zahawi
et al. currently in revision at PLOS One.

This study required the orthorectification of historic aerial photographs, as well as forest cover mapping and landscape analysis of 320 km2 around the Las Cruces Biological Station in San Vito de Coto Brus, Costa Rica. The imagery and GIS data generated were used to account for forest cover change over five different time periods from 1947 to 2014.

The datasets supplied include GIS files for:

  • Extent of the study area (shapefile).
  • Forest cover mapped for each time period (geotiff).
  • Imagery of the mosaics generated with the orthorectified historic aerial photographs (geotiff).
  • Age in studied time periods of the current forest patches (shapefile).
  • Connectivity lines inside the studied area (shapefiles).

All files are in Costa Rica Transverse Mercator 2005 (CRTM05) projected coordinate reference system. For transformation between coordinate systems please refer to http://epsg.io/5367

Aerial photographs for the years 1947, 1960, 1980 and 1997 were acquired from the Organization for Tropical Studies GIS Lab and the Instituto Geográfico Nacional of Costa Rica. The orthorectification process was done first on the 1997 set of images and used the current 1:50,000 and 1:25,000 Costa Rican cartography to identify geographical reference points. The set of 1997 orthophotos was used as a reference set to orthorectify remaining years with the exception of 1947 images.  The orthorectification process and all other geospatial analyses were done on the CRTM05 spatial reference system and the resulting orthophotos had a 2m cell size. The largest Root Mean Square error (RMSE) of the orthorectification of these three time slices of aerial photographs was 15 m.

Given the lack of information on flight parameters, and the expansive forest coverage in 1947 photographs, images were georeferenced and built into a mosaic using river basins and the few forest clearings that had a similar shape in the 1960 flyover. The 1947 set of images did not cover the whole study area, having empty areas without photographs that represented ˜12.1% of the analysis extent. Nonetheless, these areas were classified as forested given that forest was present in these same areas in the 1960 imagery.

Forest mapping was done by visual interpretation of orthophotos and Google imagery. The areas were considered forested if tree crowns were easily identified when viewing the images at a scale of 1:10,000. In areas where it was difficult to discern the type of land cover, a scale of 1:5,000 was used. This was done to eliminate agroforestry systems such as shaded coffee areas (with trees planted in rows) or very early stages of forest regeneration from the forest land-cover class. The analysis was done only in areas that were cloud free in the five time slices.  This resulted in the elimination of 134 ha (~0.4%) from of the original area outlined above. Polygons were drawn over the different areas using QGIS and were transformed into raster files of 10 m cell size.

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