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I am attempting to map several parcels just to show very basic dimensions (frontage, etc.) and parcel area. I have the parcel area from the municipal assessor's office in acres. And I have a parcel shapefile from my state's GIS entity (MassGIS) that I believe is drawn from the municipal data. There is a "Shape Area" field in the parcel shapefile attribute table, which appears to be in sq meters. I added a field for Area in sq feet, and did "calculate geometry". My problem is that the values in the attribute table for the parcel shapefile are significantly different from those provided by the assessor's office, and I am not sure whose numbers to trust. I need the dimensions of parcels to be correct, and I'm worried that the data in my shapefile is either incorrect or being skewed somehow, which will result incorrect dimensions.

Has anyone else run into this problem? Does this sound like a projection issue, or an issue with the data itself?

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    The numbers will be slightly different, your parcels are 2d and the block area was calculated in 3d by a surveyor. Additionally parcels are adjusted slightly to mesh with existing cadastre which will affect the area by a few percent without hurting the accuracy much. May 12 '16 at 2:22
  • Surveyors do NOT calculate areas in 3D! They may measure in 3D but all dimensions are ALWAYS reduced to horizontal dimensions for boundaries and area calculations.
    – kimo
    May 12 '16 at 7:41
  • What GIS software are you using?
    – PolyGeo
    May 12 '16 at 9:48
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You can add ArcGIS online map as basemap into ArcGIS desktop, to check whether your shape file is matched with the reality or not. The way to add arcgis onlie: in ArcMap->file->arcgis onLine->select the online service which is right for you(world Imagery may be ok)->click "add". enter image description here

Then your shape file will overlap with arcgis online data as below: enter image description here

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