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I have a query regarding the merging of shapefiles. I have 7 different landuse shapefiles which together covers all my study area. Now, inside my study area, there are 70 different priority areas for which I have to calculate the area of each types of landuse.

Therefore, I was thinking to merge 7 landuse shapefiles into 1 shapefile and clip the area of 70 different priority areas in order to get the area of the individual priority area (for example: 20 acre forest, 10 acre agriculture, 5 acre wetland...).

I was wondering if I would merge 7 shapefiles into 1 shapefile, is there any chance of losing any area especially on the edge of two shapefiles? If yes, could anyone suggest the right procedure so that I wouldn't lose/alter my original information of each individual shapefile.

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  • Do you mean where two shapefiles would overlap? You'll just have two features in the merged shapefile that would overlap. Won't affect areal calculations.
    – Paul
    Commented Jul 29, 2014 at 14:12
  • @Paul, yes, the overlap area. Great then. I was thinking so, but I was not sure. Thank you very much!
    – Inception
    Commented Jul 29, 2014 at 14:25

2 Answers 2

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Building on Dan C's answer, I would perform the following workflow:

  1. Merge
  2. Dissolve all shapefiles based on a common key (e.g. landuse code)
  3. Intersect your area of interest polygons with the land use polygons. This is always more efficient that clipping individual polygons and trying to extract pertinent data from the individual feature attributes.
  4. Summarize the land area by the intersect output attribute table.
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  • Thanks a lot for your systematic work flow. I was thinking to convert to a single raster after merging the shape files into one and to write python script to extract by mask based on the unique landuse code.
    – Inception
    Commented Jul 29, 2014 at 15:26
  • @Inception Alternatively, you could use Zonal Statistics as Table (Spatial Analyst) to do the work for you.
    – Aaron ♦
    Commented Jul 29, 2014 at 15:33
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No, if you're using the ArcGIS Merge tool (under Data Management Tools > General), no data will be lost. All the Merge tool does is combine all the polygons into one shapefile. If the 7 separate layers have different attribute fields, all those attributes from all 7 layers will be included in the merged layer by default.

Of course if your land use polygons overlap each other at their boundaries, and the overlapping polygons don't agree on what the land use type is present at that spot, then you'll need to reconcile that discrepancy before you can use it to assign LU types to your priority areas. You should probably use the Dissolve tool after your Merge to create one contiguous, non-overlapping layer for land use. That will only work if all your LU shapefiles contain the same attribute data fields though.

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  • @ Dan C, Thank you very much! Yes, I am going to use merge tool (under Data Management Tools > General). The attribute table of each shape file has same fields but for different area. It's really good to know that there won't be any change in area of the resulting shape file. Thanks again for your time!
    – Inception
    Commented Jul 29, 2014 at 14:31

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