Raster Cell Size differences between ArcMap and R

JoeBanker — Mon, 27 Jul 2020 13:20:34 GMT

I'm having issues when projecting habitat suitability rasters (WGS84) to a projected coordinate system (Africa Albers Equal Area Conic). The reason I reproject the rasters is so that I can calculate the area of suitable habitat which is intended to be used for conservation-related purposes.

Considering that I have about 900 individual rasters that need to be reprojected for area calculation purposes I decided to automate the process in R. However, I realised that there is a difference in 'cell size' values for the same rasters between R and ArcMap 10.7.

For example, when I use 'Raster A' (cell size: X: 0.00833333376786619; Y:0.00833333376786619) and project it to Africa Albers Equal Area Conic the cell sizes are different between R and ArcMap and therefore also the area of suitable habitat...

After reprojecting in ArcMap the cell size of the rasters are X: 879.789038737608

Y: 879.789038737608

But in R the 'cell size' is different: X: 853

Y: 902

The resampling method used was bilinear when reprojecting the raster.

This turned out to be a massive headache to me because I do not know which area calculated is the correct one as both R and ArcMap provide area estimates vastly different from one another. Area calculated from R = 18000km2 and in ArcMap 14000km2.

Any advice would be much appreciated.

Re: Raster Cell Size differences between ArcMap and R

DanPatterson — Mon, 27 Jul 2020 19:09:41 GMT

Did you explicitly set the cell size in Pro?

Cell Size (Environment setting)—ArcGIS Pro | Documentation

Cell Size Projection Method (Environment setting)—ArcGIS Pro | Documentation

You need to consider what you want for a cell size, otherwise Pro simply divides the largest of the extent width or height by 250. I have no clue what R does, maybe it uses a different random factor.

You have the opportunity to do this within the Project Raster tool directly (after reading the above and incorporating its considerations)

topic Raster Cell Size differences between ArcMap and R in Spatial Data Science Questions

Raster Cell Size differences between ArcMap and R

Re: Raster Cell Size differences between ArcMap and R