topic Re: Buffer inconsistencies in Geoprocessing Questions

Buffer inconsistencies

JM4190 — Fri, 19 Jul 2024 17:14:48 GMT

I was running a buffer on a line (1/8 mile buffer). When I went to check the distance to ensure it was correct, it was off by several units. I tried inputting it as .125 miles, as 201 meters and it was incorrect. Am I missing something? I tried measuring from edge to edge, and edge to center point, and both were off. I know the answer is probably simple, but I am stumped.

Re: Buffer inconsistencies

VinceAngelo — Fri, 19 Jul 2024 17:28:58 GMT

There's a bunch of information missing here:

What version of ArcGIS are you using? What product?
What is the coordinate system used in the display canvas?
What is the coordinate system of the Buffer source?
What is the coordinate system of the Buffer output?
Where is the data located?
What exact parameters did you provide to the Buffer command?
What is the actual measured distance?

There are many potential causes, but the most common is use of a coordinate system for which
distance is undefined, like Web Mercator.

- V

Re: Buffer inconsistencies

JM4190 — Fri, 19 Jul 2024 17:54:54 GMT

Thanks for the reply Vince.

I am using ArcMap
I was projecting the line segment in State Plane FIPS 1900
This is the data frame coordinate info:
- NAD_1983_2011_StatePlane_Maryland_FIPS_1900_Ft_US
  WKID: 6488 Authority: EPSG
The projected buffer coordinate is this:
- Projected Coordinate System: WGS_1984_Web_Mercator_Auxiliary_Sphere
  Projection: Mercator_Auxiliary_Sphere
Not sure what you mean by where the data is located. its saved onto my desktop.
I didn't set it to any other parameters other than the .125 mile buffer distance

Re: Buffer inconsistencies

JM4190 — Fri, 19 Jul 2024 17:59:34 GMT

and from center to edge i get .19 miles.

Re: Buffer inconsistencies

VinceAngelo — Fri, 19 Jul 2024 19:27:39 GMT

Measurements in Web Mercator aren't really in meters. The poles are infinitely far from the Equator, so distance accuracy is wrong to start (sphere), and gets worse as latitude magnitude increases (at roughly tan(latitude)). Never measure ANYTHING in Web Mercator, because it can't give a correct answer. If you're working in MD State Plane, keep on using MD State Plane to get accurate distances.

- V