topic Re: Distance in Buffer Calculation - Not Accurate in ArcGIS Pro Questions

Distance in Buffer Calculation - Not Accurate

Robswann — Fri, 03 Sep 2021 17:07:36 GMT

For some reason my buffer distance for a attribute rule is very inaccurate. I have tested this with the code below, and for an example, Features that are within 1 mile of school districts layer are not being counted. Any help would be appreciated.

var Districts = FeatureSetByName($datastore, "SCHOOL_DIST")
var Buffer1mile = buffer($feature,1,'mile')
var Districts_Within_Search_Radius = INTERSECTS(buffer1mile,DISTRICTS)
VAR NO_OF_SCHOOLS = COUNT(Districts_Within_Search_Radius)

Count(districts_within_search_radius )

Re: Distance in Buffer Calculation - Not Accurate

JayantaPoddar — Fri, 03 Sep 2021 17:17:43 GMT

Could you try using BufferGeodetic() ?

Re: Distance in Buffer Calculation - Not Accurate

David_Brooks — Fri, 03 Sep 2021 17:24:14 GMT

@Robswann are you working in Web Mercator auxiliary sphere by any chance? Change to a national projection system and rerun the buffers to confirm that's the issue.

Buffering in WMAS is a nightmare, so you'll need to switch to geodetic method of buffer if you need to stay in that.

Re: Distance in Buffer Calculation - Not Accurate

Robswann — Fri, 03 Sep 2021 17:41:52 GMT

OK i have tried both suggestions. I was working with WMAS, and changed it to NAD 1983. I am still getting inaccurate returns. For some reason, when I input the buffer geodesic it returns an error. Again thanks for the help

Re: Distance in Buffer Calculation - Not Accurate

David_Brooks — Fri, 03 Sep 2021 17:58:22 GMT

If your data is in Web Mercator, try reprojecting it to NAD1983 also change the system of your map.

Re: Distance in Buffer Calculation - Not Accurate

DanPatterson — Fri, 03 Sep 2021 19:25:25 GMT

Nad83 is a datum... do mean a UTM or State Plane etc with a NAD83 datum?

Re: Distance in Buffer Calculation - Not Accurate

David_Brooks — Fri, 03 Sep 2021 19:27:45 GMT

@DanPatterson , great point, i wasn't clear in my reply. You need to change the coordinate system into a projected system in either UTM or state plane (local system to your area)

Re: Distance in Buffer Calculation - Not Accurate

Robswann — Fri, 03 Sep 2021 19:36:19 GMT

I have all layers and map in the NAD 1983 StatePlane Texas S Central FIPS 4204 (US Feet), Should I try a different Coordinate System?

Re: Distance in Buffer Calculation - Not Accurate

JayantaPoddar — Fri, 03 Sep 2021 19:55:19 GMT

Does your original script return any count at all? Please check with 10 miles of buffer distance. If it doesn't, there is issue with the script.

Re: Distance in Buffer Calculation - Not Accurate

Robswann — Fri, 03 Sep 2021 20:01:21 GMT

Yes it is returning a count.

It should return a 1 when the polygon is not within 1 mile of a school district.

If it is 1 mile within a school district it should return 2. (The school district is located in, and the school district within 1 mile)

Re: Distance in Buffer Calculation - Not Accurate

Robswann — Fri, 10 Sep 2021 15:55:59 GMT

I finally got it working by changing all spatial references, It took a while but now I am using geodesic, and its working as it should. Thanks for everyones help