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I am trying to create a buffer around different series of lines. I have a polylines file with 1 location shown below:

enter image description here

I want an equal spaced buffer that is dissolved around all the lines at this location spaced 812 meters from any given end point (end points of along outside lines). I imagine this should look almost like a pillbox. However, when I run the buffer tool, this is what I get:

enter image description here

Obviously that does not look correct. It is not symmetric. When I have a large shapefile that contains many sets of lines, all of the buffers have slightly different shapes. All groups of lines have the same spacing and distances. I am not sure if this has to do with orientation because if the lines run N/S or E/W, the buffer is almost correct:

enter image description here

This is almost what it should look like, but the spacing on the sides is a lot closer than the spacing on the top.

I thought it may be an issue with dissolving the group of lines together so I tried making a rectangle around the lines so it would be 1 object:

enter image description here

However, this just created the same exact incorrect buffer I provided earlier.

Does anyone have any suggestions as to how I can create this buffer I am looking for?

As a side note: I need this buffer around all the transects together and cannot just take the centroid of these lines and make a circular buffer.

PolyGeo
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user25819
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1 Answers1

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Blord-castillo hit the nail on the head with the comment about the projection. I've run into this "problem" before and there are 2 answers that I know of:

Option 1) Your results from the incorrect-looking buffer really are correct! This is a normal effect of setting your dataframe coordinate system to a geographic coordinate system, I'm attaching a picture of how this works with a single dataset that is displayed 2 different ways. Note that the projection of the dataset doesn't matter, what matters is the coordinate system that you set in the dataframe properties.

Option 2) I think this is unlikely, but it's possible that your results really are incorrect. This used to be a more common problem in ArcMap, when doing analyses on different projections of data could lead to an incorrect result because somehow the projection-on-the-fly wasn't working out correctly. Thankfully this has become much rarer. The solution there used to be to make sure you have a projected (not lat-long!) dataset and that you are working in a projected dataframe coordinate system in ArcMap.

Option 3) Something entirely different? your 'warp' direction is the opposite of mine, I think this could be the case if you're working with Southern Hemisphere data and I'm working with Northern Hemisphere data? or else something funny is going on.

How to tell which answer is correct? You can either change your data frame -> properties --> coordinate system in ArcMap to a projection that doesn't warp features. Geographic (lat-long based) displays will warp features, many other common projection displays will not warp when displayed at local scales... though as you can see from the example many common projections will rotate features some. Or you can use the 'measure' tool, and check the actual distances going around the feature to the buffer line, just make sure the units are set to some ground-based units like meters and not to decimal degrees. MapShowingBufferDisplayedInUtmAndInGeographicCoordinates

user2065766
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