OK, probably not a projection issue. Have you tried Snap (editing)? Or maybe Integrate, though this one doesn't see quite right for you. I found these by searching 'snap' in my geoprocessing tools.
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Have you tried closing and reopening ArcMap? And have you looked for the density raster in the default current and scratch workspace locations?
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If the polygons and points disagree by hundreds of feet that might be a projection issue. Could you share the projection information for both the polygon parcel and GPS point layers? You might also want to double check that both layers are in either feet or meters and that the projection is the same as the data frame's projection. -Josh
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