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| GeoCommunity Mailing List |
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| Subject: | Re: [gislist] "summarize by" question |
| Date: |
04/26/2005 11:15:01 AM |
| From: |
True, Cynthia D. |
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If your parcels were perfectly square and lined up with the grid cells,
you would get the same answers for area. Long, narrow, curvy polygons
have more deviations from the square grid cell model, and therefore have
a greater difference in area. If you need a "closer fit" in area
calculations, you can make your grid cells smaller.
Good Luck,
dt
-----Original Message-----
From: gislist-bounces@lists.geocomm.com
[mailto:gislist-bounces@lists.geocomm.com] On Behalf Of Julia Reisemann
Sent: Tuesday, April 26, 2005 11:02 AM
To: "GIS List (E-mail)" slist
Subject: [gislist] "summarize by" question
I have a question regarding the Summarize by in ArcView. I noticed that
a summarize by on a shapefile gives me higher numbers than summarizing
the same data as a grid (can be a much as 5%). The file is a parcel
file, the grid to summarize on has 30m gridcells. Does anybody know,
why ArcView does this? I assume there is a difference in the algorithm
or the problem of having a shapely parcel file in contrast to a straight
forward grid. Would be great, if anybody really knows what is going on.
Thanks,
Julia
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