I'm using population density data, 2.5' grid. My question is -- If a small populated island is the only land in a given cell, and its area is smaller than the cell's, how is the population density for the cell computed? Is the population of the island distributed over the whole cell's area? Or is the population density of the island applied to the whole cell?
The population density for the GPW grids is based on actual land area (net of permanent ice or water) within a grid cell or cells. Small islands that are less than one cell will have a land area that is less than the size of the 2.5 arc-minute cell. This value (in square km) is recorded in the land area grid for the country which is available from the download page of the GPW site. This is also true for coastal cells that are part land and part water.