topic Re: Buffering From The Edges Of A Polygon in Geoprocessing Questions

Buffering From The Edges Of A Polygon

DavidMeek1 — Fri, 13 Dec 2013 15:13:49 GMT

I'm trying to create a buffer zone from a set of irregular polygons, and the distance needs to be measured outward from the edges of the polygons, NOT the centroid. Can this be done?

Thanks for the help!

Re: Buffering From The Edges Of A Polygon

michaelcollins1 — Fri, 13 Dec 2013 15:26:53 GMT

Isn't that what the buffer tool does anyway?

If you just need the outside buffer, select "OUTSIDE_ONLY" for Side Type

Re: Buffering From The Edges Of A Polygon

DavidMeek1 — Fri, 13 Dec 2013 16:13:16 GMT

Well, I thought so too, but not in this instance. I'm using NAD27, State Plane 4204, US Feet and attempting to put an 8,000' buffer around county abstracts. When I measure the distance from the edge of the polygon to the edge of the buffer, I'm getting about 6,880'.

Re: Buffering From The Edges Of A Polygon

michaelcollins1 — Fri, 13 Dec 2013 16:19:43 GMT

can you post part of the shape file?

Re: Buffering From The Edges Of A Polygon

RobertBorchert — Fri, 13 Dec 2013 16:21:05 GMT

You need to determine for sure that your referencing feet and not another unit in your data frame.

Try it with the buffer analysis tool instead. there you can specify which units to use.

Well, I thought so too, but not in this instance. I'm using NAD27, State Plane 4204, US Feet and attempting to put an 8,000' buffer around county abstracts. When I measure the distance from the edge of the polygon to the edge of the buffer, I'm getting about 6,880'.

Re: Buffering From The Edges Of A Polygon

DavidMeek1 — Wed, 18 Dec 2013 12:11:11 GMT

No luck so far.

The data frame coordinate system is:   NAD 1927 StatePlane Texas Central FIPS 4203
Linear Unit in that system is: Foot_US

I'm selecting a buffer linear unit of: 8,000 Feet

I'm still getting a buffer zone about 6,880 feet deep from the outside of the object to the outside of the buffer zone. That's using both the internal MXD toolbox and also using:
Arc Catalog
   System Toolboxes
      Analysis Tools
         Proximity
            Buffer

Re: Buffering From The Edges Of A Polygon

DaleHoneycutt — Wed, 18 Dec 2013 21:06:15 GMT

Most likely, the data frame coordinate system and the coordinate system of the features are different.

But all this can be avoided if you've got 10.1 -- you can instruct the buffer tool to do geodesic buffering by setting the Output Coordinate System environment to use a geographic coordinate system rather than a projected coordinate system. Have a good look at the tool documentation. Here's the 10.1 doc for Buffer.

If you don't have 10.1, then double check that the coordinate systems of the data frame (used by the measure tool) and the coordinate system of the feature class (used by the buffer tool) are exactly the same.

Re: Buffering From The Edges Of A Polygon

DavidMeek1 — Thu, 19 Dec 2013 14:22:28 GMT

Thanks to all for your replies!

You were correct that the problem lay in the coordinate systems used in the various layers. Everything is taken care of.

David