Thursday, December 15, 2011

Projection weirdness in ArcGIS and at AGO


I've been working with Philadelphia Public Safety to look at our ArcGIS Server map services in ArcGIS Online maps.  Our points were plotting over central Africa, not Philadelphia.

Obviously, we suspected that part of the problem must be the Penna State Plane coordinate system that we use.  One weird clue was this:  When we added the PPS basemap (Penna State Plane) as basemap to the AGO app, the point layers plotted ok.  But if we used the Esri basemaps that are default on AGO, the points float over Africa.

We compared the few data layers that displayed ok, against those that didn't.  We found that the bad map layers didn't have the right coordinate system listed in the Data Frame Properties in ArcMap.   We tried different scenarios to fix this.  The point layer was created as an XY Event Layer.  If we added this first to the ArcMap Data Frame, the coord system would not register correctly to the Frame.  We had to first add the PPS basemap (Penna State Plane) to the map, then create the point layer, then remove the basemap before publishing the service to ArcGIS Server.

We don't understand why.  Do you?  Leave a comment. 

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