ePressure is providing various means to assess pressures on protected areas

1. Population pressure

Population data were obtained from the Gridded Population of the World data version 3 (GPWv3), which depicts the distribution of human population across the globe. GPWv3 provides globally consistent and spatially explicit human population information and data in a raster format. The data set is constructed from administrative units of varying resolutions and the native grid cell resolution is 2.5 arc-minutes, or ~5 km at the equator, although aggregates at coarser resolutions are also provided. We use here separate grids made available for population count and density per grid cell.
Population data estimates are provided for 1990, 1995, and 2000, and projected (in 2004, when GPWv3 was released) to 2005, 2010, and 2015.
The data are made available by the Socioeconomic Data and Applications Center (SEDAC) http://sedac.ciesin.columbia.edu/data/collection/gpw-v3

1.1. Population Pressure Index

Population pressures on a protected area were estimated using the Gridded Population of the World map for the year 2000 and a cost-distance function to quantify accessibility to the protected area and a buffer zone around each protected area. The cost distance function was derived from information on slopes, roads, rivers, land cover and international boundaries to compute a travel time from each point of the boundary of the protected area (Nelson, 2008). In other words, thematic maps were converted into gridded data where each cell receives a weight reflecting the pressure level on the protected area. A land cover map, for example, can be used to derive an accessibility map to a protected area by attributing high values to obstacles (rivers, mountains, hills) and low values when the terrain can be easily crossed (e.g. savannahs, grassland) as illustrated in Figure 19. As a result, a buffer area representing 3 hours of traveling could be delineated around each protected area and further used to calculate the average population density. This average population density in the buffer area is the Population Pressure Index.

1.2. Index of change in population pressure

The Population Pressure Index is available at different time steps, and this allows us to evaluate changes in population pressure around a PA. Here, PAs are ranked by the percentage change in population pressure between 1990 and 2000. The percentage population change is the percentage change in this computed metric between 1990 and 2000, with the 1990 value as a baseline.

2. Agricultural pressure

The Agricultural Pressure Index is based on the average percentage of cropland in 1 km raster cells within a 30 km buffer zone around protected areas, aggregated to a single metric using an inverse distance weight function. The IIASA-IFPRI cropland percentage map for the baseline year 2005 (Fritz et al., 2015) was used to identify the percentage of cropland in each cell within the buffer

3. Pressures from roads

Data on roads was derived from the Global Roads Open Access Data Set (CIESIN, 2013). The data is generated by the Center for International Earth Science Information Network - CIESIN - Columbia University, and Information Technology Outreach Services - ITOS - University of Georgia and available from http://sedac.ciesin.columbia.edu/data/set/groads-global-roads-open-access-v1
The road data was rasterised to 500 m resolution and then used to identify roads globally. Road pressures were calculated based on the percentage of cells with presence of roads inside protected areas (Internal Roads Pressure Index) as well as within a 30 km buffer zone around protected areas (External Roads Pressure Index), using an inverse distance weight function. The pressure values are normalized by country only, not by ecoregion, due to differences between countries in the density and detail of the road data supplied.