If they have a different Geographic Coordinate System then look at Transformations in the Data Frame Properties and make sure the correct one is set for transforming the GCS of the new layer to that of the Data Frame and presumably of the original layer. If they are the same CRS then the GIS source has made some error in the new file or corrected some error in the old. The magnitude of the displacement is typical of an incorrect GCS transformation, but to confuse that you mention that the displacement is variable.Īlso, I'm not sure what you mean by " Both shapefiles are projected on NAD 1983 in zone 18N ": do you refer to the Data Frame projection or the CRS of the files as shown in layers Properties > Source or in ArcCatalog under the shapefile Properties XY Coordinate system ? Good luck, I'll look forward to seeing how this mystery turns out. Clearly, they did not do any ground truthing. Maybe they just mixed up data from a recreational GPS rather than an RTK or survey GPS. Once you contact the contractor you could also go through the steps they took to see if someone did a transformation from WGS84 to NAD 1983 and used a wierd algorithm. It seems especially glaring in view of the obvious variable displacement from Google Earth imagery which shows lot lines (sidewalks, fences etc.) in Pembroke so clearly I could see drawing them straight from that.Īnyway, it would be educational if you have the time to go through the steps of checking the ground point surveys in the new photomosaic, look at how the photos were orthorectified and mosaiced and see if you can spot the error. This would be a case for going back to the contractor and getting them to fix it. However, it seems just a bit disturbing that the new orthophotos and the shapefile drawn from them ARE inaccurately georeferenced. Parcel fabrics may not be legal lot surveys, but they should be as accurate as possible. You might also consider regeoreferencing the new photomosaic and then spatially adjusting the new shapefile to match, but again same deal. Another alternative would be to use the spatial adjustment tool and shift the whole thing to match your old shapefile, but this would apparently involve some rubbersheeting so I'd be hesitant to waste my time fixing a contractors error. to copy it over one parcel at a time or use a spatial join and add attribute fields to your existing shapefile. If there is new information in the New parcel shapefile pertaining to existing parcels then you can use the attribute transfer tool. I wasn't able to do anything with the xml file you posted, but it sounds like you've resolved things anyway with the news that the original was drawn from survey plans. AND to boot, it is also important since you've noted that all sorts of utilities layers are based on the same datum. If you have confirmed that the old parcel shapefile is accurate then you should stay with it, period. Question: how do I re-align these so they match?Ĭan anyone explain why the 'correct version''s coordinates do not match those of Google Earth? If I have left any information out that might help solve the problem please let me know and I will do my best to answer. When comparing the same google earth coordinates to the same point on the new land parcels layer they differed by 3m and 8m for Eastings and Northings respectively. Some places line up well but others are skewed, either to the north east, south east, you name it.īoth shapefiles are projected on NAD 1983 in zone 18N, and when comparing some coordinates on the original map to coordinates on google earth (plotted on WGS 84)they were a close match - 0.5m difference. Some of the parcel's edges were misaligned by up to 20 metres in some places.īiggest issue - not a uniform misalignment. This would not usually cause any problems but when I uploaded the new shapefile and placed it over the existing one, the road edges and property lines did not line up. This update is in fact a new shape file that I am to replace the old shapefile with. I have been given an updated version of the land parcels layer for a geodatabase that covers the company's service area (From Hunter GIS).
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