raster_runif: a raster with random values between 0 and 1 for every cell of the datasource GRTSmaster_habitats

The <code>raster_runif</code> data source covers the Flanders and Brussels region and has a resolution of 32 meters. The raster cells with non-missing values match the value-cells of the <code>GRTSmaster_habitats</code> data source with a small buffer added. Every raster cell has a random value between 0 and 1 according to the uniform distribution. An example usage of this raster is its combination with the <code>GRTSmaster_habitats</code> and <code>habitatmap_stdized</code> data sources in order to draw an equal probability sample of habitat types in Flanders. <code>Habitatmap_stdized </code>contains polygons that are partially or fully covered by habitat types. The proportion of a certain type within a polygon is provided by the <code>phab</code> value. We can draw an equal probability sample size <em>n</em> for a certain habitat type as follows: select all raster cells of <code>GRTSmaster_habitats</code> that overlap with the sampling frame of the target habitat type keep the raster cells for which the <code>raster_runif</code> value is lower than the <code>phab</code> value of the habitat type within the polygon finally select the <em>n</em> raster cells with the lowest GRTS ranking number. The R-code for creating the <code>raster_runif</code> data source can be found in the GitHub repository 'n2khab-preprocessing' at commit ede43a4. A reading function to return the data source in a standardized way into the R environment is provided by the R-package n2khab.