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I am relatively new to GIS.

I need to define small areas (manually draw them out) within a buffer zone around a point. After they are drawn out I need to quantify how much of the buffer zone (1 mile from point) these drawn areas take up in total.

I have a ortho high-res map layer as well as a shapefile from the census. I also have several points geocoded for this project.

Can anyone help with the process of:

  1. using the edit feature to draw out areas around the geocoded point. I have been able to create polygons but not sure how to create a feature that merges all drawn polygons that I am drawing as one feature.
  2. seeing how much area these manually drawn areas take up in a buffer zone around the geocoded point.
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    What GIS Software? – Mapperz Aug 8 '16 at 18:53
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    I am using arcmap. As of now I think I may have found the solution. I have created a new shapefile layer where I will be creating the polygon shapes and then using a Union with that layer and the buffer layer I have created around the points I can see how much area those polygons take up. Do you see any potential issues with this method? – Dpatel87 Aug 8 '16 at 22:05
  • This is what I suggested in my answer, so yes it will work. – jbalk Aug 9 '16 at 3:40
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  1. Start editing. In the editor toolbar, there is a dropdown menu. Select all your features you want to merge, click the editor dropdown menu, select 'Merge', select the feature to merge on (will take the attributes of the merge feature and discard the rest). enter image description here
  2. Add a field of type float to the manually drawn feature class. Right click on this field and select 'Calculate Geometry', select area, and the units you want. Do the same thing for your buffer. Divide the area of the manually drawn area by the area of the buffer and multiply by 100% to get percentage.

enter image description here

If your manually drawn areas do not entirely overlap your buffers, you can run an intersect or union to split the polygons where they overlap, then run the area calculations.

Update: Forgot to specify that I am using ArcGIS 10.3 to do this. This can also be done in QGIS, but my examples are from ArcGIS.

  • This is great, and exactly what I was looking for. Thanks so much for the help – Dpatel87 Aug 9 '16 at 14:32

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