Misaligned Land Parcel Update

[EricRoot]

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). This update is in fact a new shape file that I am to replace the old shapefile with. 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. Some of the parcel's edges were misaligned by up to 20 metres in some places.

Biggest issue - not a uniform misalignment. Some places line up well but others are skewed, either to the north east, south east, you name it.

Both 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. 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.

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.

Question: how do I re-align these so they match?
Can anyone explain why the 'correct version''s coordinates do not match those of Google Earth?

Any help is appreciated!

[EricRoot]

The contractor has simply stated that the original shapefile is incorrectly laid out, they did not offer any type of solution so I thank you for all of your help.

I have decided to use the Spatial Adjustment tool, using the rubbersheet option. I spent the last day working on moving each corner of the land parcels and after adjusting there are still some errors. I noticed that if I move one land parcel the parcel across the street may be affected. What I am doing now is aligning each corner of each land parcel - a very tedious process.

Would you have any tips or suggestions on how to decrease my work time? Maybe even some sort of keyboard shortcuts?

[HardolphWasteneys]

Eric,
frustrating business ...

offhand suggestions regarding a wholesale spatial adjustment would be:
1. work from copies of the original
2. review the help sections on spatial adjustment thoroughly
3. review the use of snapping

As you observed, rubbersheeting the whole thing can lead to frustrating iterative effects and you may be better off shifting sections of parcels and snapping them to your old ones.

All that being technically feasible, the contractor's statement that the original shapefile was not correctly laid out seems ambiguous in light of the incorrect georeferencing of the photomosaic they used, unless they were given the photomosaic as is.   I'd get clarification of that from them.   I don't know how much is at stake in the new shapefile or what the intent was, so it is hard to recommend a course of action, but I'd resolve the georeferencing of the photomosaic first.  If the new shapefile covers the same parcels as the old one only and with the same attributes, I'd be tempted to abandon it, but I have not seen either except in glimpses from the screen shots.   If you adjust the new file the photomosaic will no longer be useful as an underlay for new development areas.  At least it is just Pembroke and not all of Ottawa or Toronto.

So to reiterate:  I'd not recommend spatially adjusting the new shapefile until you have resolved the georeferencing of the photomosaic.  Get the ground control points and double check their coordinates and that they were used correctly to georeference the photos.  If there was an error in that find out who was responsible.  If the GIS contractor was only responsible for drawing the shapefile they might be off the hook, but it seems byzantine to me. 

If you want to upload the two shapefiles, copy them into a new folder in ArcCatalog and see if you can upload that here as a unit or send them to me directly at my e-mail and I'll have a look.  As I said I could not do anything with the xml file alone.   The photo raster is probably too large.

looks like you've done a thorough job so far.

Hardolph

PS. as an afterthought on spatial adjustment in case you really get stuck into it:  avoid rubbersheeting as much as possible and minimize the offset you use if you do by first finding an absolute offset that comes close as possible by using the editor MOVE function to shift all the polygons by some measured and recorded amount (e.g. 3m west and 5m south), or attempt to use a Projective transformation.  Again work from copies and if it screws up ditch it and start again.  Rubbersheeting should be your last resort.  
  H

[EricRoot]

I have successfully oriented all parcels to be aligned with the previous (older) layer, using the rubbersheet method. I ensured that the other layers were being transformed as well.

The limited adjustment tool allows the user to draw a polygon around a specific area to set boundaries for rubbersheeting. Anything outside of the polygon will not be affected. This is how I was able to line up the layers precisely.

Now I have to transfer the attributes and set the symbology in my new layers to match the utilities symbology.


I am using ArcMap10.

[EricRoot]

Hey,

I was able to get through the entire city, any new parcels or shapes I did not join to but would use the edge snapping tool to get close. If there was a curve vs a point I would rubbersheet the edges until the beginning of the shape so that it would best fit. There area few small areas of interest, such as hydro lines getting a little close together, but as I use the map I will work out the kinks. I will be using the shapefile you have created in place of the PembrokeParcels_ORC to maintain data, and I thank you for providing me with this.

If I simply used the rubbersheet on the corners a complex area the polygon gets deformed. In the example I attached (as I did for the rest of the city) I placed displacement links on all corners of all polygons if they had a corresponding parcel on the other layer.

I have showed my employer that some buildings are somewhat deformed - skewed building edges on some - and they are happy with the results. For the most part the building polygons maintained their shape, reason being: I placed links on all corners and so the shape of the polygons did not change, just the orientation.

Thanks again for all of your help.

Eric