Raster Cell Size differences between ArcMap and R

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07-27-2020 06:20 AM
JoeBanker
New Contributor

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.

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DanPatterson
MVP Esteemed Contributor

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)


... sort of retired...
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