Inconsistent Select By Location behavior

Discussion created by GlennK on May 15, 2013
Latest reply on May 21, 2013 by jamesfreddyc
For the purposes of discussion, building a Topology is not an option, otherwise this exercise would be easy.

I am performing the same Select By Location two different ways.

The first method, let's say Method A, is performed manually, using the Select By Location icon in ArcMap. I am selecting line features from LayerL that intersect point features from LayerP. A review of the selection seems to indicate that results are accurate and expected.

The second method, let's say Method B, is performed via a Python script. Below is a code snippet

lyrL = arcpy.GetParameterAsText(0)
lyrP = arcpy.GetParameterAsText(1)
arcpy.SelectLayerByLocation_management(lyrL, "INTERSECT", lyrP, "", "NEW_SELECTION")

Method B does *NOT* return the same selection as Method A. The results of this selection are dubious, as many line features are not selected that do, in fact, intersect points, as well as many line features that are selected that do NOT intersect points.

I am thinking this might be a tolerance issue, but I can't find anything to support my theory. Anybody have an idea why this is, or has anybody experienced this before?