I have a raster layer (chlorophyll concentration) and a non-overlapping layer of polygons (regions of the ocean). For each polygon, I'd like to find the area where the majority of chlorophyll is concentrated – e.g., the smallest area covered by 80% of the total chlorophyll in that polygon. I cannot think of an elegant way of achieving this, however. I have access to both ArcGIS (10.1) and QGIS (2.8 Wien), so a solution with either is fine.
One crude approach is to start at a high threshold value and calculate the amount of chlorophyll above that threshold for each polygon, then turn to that into a percent of the total chlorophyll for that polygon. Incrementally, I decrease the threshold until I reach 80% for each polygon and calculate the corresponding area. This is horrifically cludgey and I know that there must be a more efficient solution. Is there a better way of doing this is ArcGIS or QGIS?
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One crude approach is to start at a high threshold value and calculate the amount of chlorophyll above that threshold for each polygon, then turn to that into a percent of the total chlorophyll for that polygon. Incrementally, I decrease the threshold until I reach 80% for each polygon and calculate the corresponding area. This is horrifically cludgey and I know that there must be a more efficient solution. Is there a better way of doing this is ArcGIS or QGIS?
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