# Calculating combined area of multiple polygons by counting overlapping area only once in R?

I'm using a shapefile in which polygons represent the geographic distribution of species. I need to calculate the combined range of several species sets, but the overlapping areas should be counted only once. My initial solution was to dissolve the polygons of the set of species of interest and then calculate its area. However, I must do this with more than 2000 sets of species and some of them have up to 10000 polygons, making the analysis take too long.

Is there another faster or more practical way of calculating the combined area of a set of polygons by counting overlapping areas only once?

For example, is there any way to delineate the outer contour of overlapping polygons?

I'm conducting these analyzes in R, but I'm willing to use other software if it decreases computational time considerably.

• Welcome to GIS SE, please take tour and edit your question. Add the code that you have been developed at the moment and some images showing the desired output. For vector processing, I would use QGIS, or a mix process between R and QGIS – aldo_tapia Feb 15 '18 at 12:32
• When you use dissolve in QGIS natives you've got to have a topologically clean shapefile, and may come out with errors; ogr2ogr (gdal tools may be better, and you can also use it in R with rgdal); arcmap is quite a blacbox and it dissolves quickly within the program, but takes very long when you ask it to export the result... and there's always parallelization in R, so you run the process in a lot of cores, library raster has it – Elio Diaz Feb 15 '18 at 16:04
• I do not know if I completely understood your question, but I think maybe this could help: r-spatial.github.io/sf/reference/geos_binary_ops.html. In particular, have a look at `st_intersection` – lbusett Feb 16 '18 at 9:41