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I have a shapefile of irregular polygons and a GRID (both as raster and polygon grid). How can I count the AREA SUM of irregular polygons per grid cell?

Can use ArcGIS, QGIS or R.

(Application: Nation rasterized into GRID. Question: How much area of what type of protected area in each raster cell?)

Thank you,

Florian

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Can you clarify: How do you want to handle polygons that do not completely lie within a grid cell? Do you want to include only the portion of their area that lies within the cell? –  MappaGnosis Jan 31 '12 at 7:40
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1 Answer

Here's a solution using ArcGIS. Union the national polygon with the polygon grid and call it Union. If the Union dataset is not in a geodatabase, create an "area" field and calculate the area of the polygons. Then dissolve Union, using the unique ID field of the grids (not the FID or OJBECTID, but the FID_grid or OBJECTID_grid field) and the protected area field as the dissolve fields. If the dissolved dataset isn't stored in a geodatabase, then add the area field in the statistics fields, using the SUM statistics type.

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You could alternatively add the area field at the end of all the processing and perform a Calculate Geometry on the final feature class. (Or if you're working in a geodatabase, the area will be automatically calculated for you, using the default area unit of the projection your features are in -- usually square meters or square feet.) –  nmpeterson Jan 31 '12 at 17:50
    
I had thought about that, but the Dissolve's statistics fields option does both steps for you. –  kenbuja Jan 31 '12 at 18:11
    
My main problem with doing it that way -- and it's only a problem because I'm anal about such things -- is that you end up with a fieldname like "SUM_Area". To get one called, simply, "Area" you would have to create a new field, populate it with the values from SUM_Area, and delete the SUM_Area field. But Esri's inept inability to enable the simple renaming of fields is another topic entirely. –  nmpeterson Jan 31 '12 at 18:43
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