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I'm using Select by Location to find wind turbines within 5-km of a center point feature -- why does this command also select nearby turbines?

The image below shows my selected points with a 5-km buffer circle drawn for comparison. As you can see, turbines that are not even close to touching the circle are included.

enter image description here

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    Are both in the same spatial reference? Are you trying to select geographic features with a projected circle or the other way around? In the select by location dialog have you got the 'buffer' checked? – Michael Stimson May 19 '15 at 1:45
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    Are they single points or multi-points (or multipart features)? What coordinate systems are you working with *data layers and data frame)? Version of ArcGIS? Using Cartesian or Geodedic distances/buffers? I suspect it's a simple you're in geographic coordinates and need to be in a projected coordinate system. – Chris W May 19 '15 at 1:45
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    I think either of the above comments could lead to these symptoms so I think we need you to edit your question and provide precise details of the steps you take from starting ArcMap and adding in the data - with details of where the data is stored and in what coordinate system. – PolyGeo May 19 '15 at 1:59
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    That could be it, to keep things uniform the selection is done in the coordinate system of the data frame. Try changing the spatial reference to match the data. Can you confirm that they're not MulitPoint features? If this problem persists you can use a tool like Near (advanced license) or Generate Near table (again advanced license) to determine the distance of each point to the closest (or all) wind farm points then select by attributes (NEAR_DIST < 5000) – Michael Stimson May 19 '15 at 2:10
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    Yo -- thanks for the thoughts about projects. I changed the data frame's PCS to match the Layer's PCS (N America Albers) and it now seems to work much more accurately. Thanks Stackers! – Nick Cain May 19 '15 at 20:48
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"multi-points" (you can check in the geometry field) behave like single geometries. You can convert from multi-point to points using "multipart to single part" tool, then you can run your "select by location" within a distance. If needed, you can then dissolve the points based on the original ORIG_ID in order to reconstruct the multi-points.

The other option is to create the buffers around your wind farm, then intersect with your multi-points (the output will be multi-points).

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