“My point buffers are’t round.” “No problem sir, that is an ArcMap design feature.”

Wednesday, April 2, 2008 at 06:20:26

One of my MSc students was recently completing a piece of coursework that required finding a solution to a spatial task, part of which involved the creation of buffers. He noticed that the buffers created around points in ArcMap weren’t round (giving a significantly different solution to MapInfo) but rather oval and so decided to investigate further. His answer came in the form of this technical note from ESRI:

ArcMap Buffer Wizard produces buffers that are not round

As this note describes, by default ArcMap uses the Hotine projection to calculate buffers and doesn’t recommend its use at high latitudes or distances over ~5 miles. I find this an amazing default behaviour. My expectation would have been to perform the buffer in the same projection as the input Data Frame however this is not the case. In fact it appears to be a hard coded setting in the registry that is only changeable by using the AdvancedArcMapSettings utility.

Of course this raises more questions. Why the Hotine projection? Does it effect ArcView 3.x or ARC/INFO prior to the release of ArcGIS? I thought that ArcView 3.x used a different algorithm to calculate buffers (through the GeoProcessing Wizard) than ARC/INFO. This Wizard (in UI form anyway) was ported to ArcGIS, whilst buffering was also available from ARC/INFO in ArcTools. So are the 8.x and 9.x buffer algorithms different?

For such a fundamental algorithm to have this default behaviour is quite worrying and one wonders how many studies have incorrect buffer calculations.

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