Projecting data correctly in Arcgis basemaps.

[ClintonSpencer]

I loaded some data onto the basemap, but it is off by about 100 feet. is there anyway to correct this?  My data is in NAD27.  Thanks.

[MikeMinami]

What kind of data are you adding to your map?

Thanks,

Mike

[ClintonSpencer]

I am trying to add zipped shapefiles.

[MikeMinami]

it's probably best to transform your data into WGS84 Web Mercator Auxiliary sphere first.

Thanks,

Mike

[ClintonSpencer]

Okay, so that got is close, but we're still off by about 20-30 feet.  Is that typical?

[MikeMinami]

Well, there is some rounding going on during conversion, but this offset seems too big. Do you have ArcGIS Desktop? When you display the shapefile in desktop over the same basemap data, do you see the same offset?

Can you share your shapefiles with us? Both the original and transformed versions? Perhaps you can clip out a small piece of it if the data is large.

Thanks,

Mike

[JimWatts]

Hi,
We are having the same problem with the Bing basemaps near approximately 45 Degrees S latitude.
The original thought was that because of the mercator projection, we were seeing a 10 m offset in the Bing basemap, however, when we projected into the WGS84 Web Mercator sphere, the problem didn't go away. We know the shapefiles we have are correct because they match all other data sources.  We are using ArcGIS Desktop (ArcINFO licence) Version 10.0. The original polygon layer that we are working with is in WGS_1984, and we are just using the "On the fly" projection to visualize those in the WGS 1984 Web Mercator projection.  The points that are out by ~ 10 meters are in NZGD 2000 New Zealand Transverse Mercator. We have tried re-projecting the points and polygons to Web Mercator, but still see the same offset, so it is likely that the problem is the Basemap, not the points/polygons.

Is there a way to correct the offset in the Bing maps?

One thought was to rasterize the Bing map so we can use the "Shift" tool and put it into the correct orientation, however, we are unable to figure out how to do that.

Do you have any tips for doing this?

Cheers

[MikeMinami]

Jim,

Are you seeing the 10m shift when displaying in ArcGIS Desktop? Or in ArcGIS.com map viewer? Or both?

Thanks,

Mike

[JimWatts]

Hi Mike,

We are seeing the 10m shift displaying in ArcGIS Desktop. Haven't tried it in ArcGIS.com. Should I re-post this in the ArcGIS Desktop Forum?

Cheers


Jim

[MelitaKennedy]

Hi Clinton,

When you converted to Web Mercator Aux Sphere, what transformation did you use between NAD27 and WGS84? Is the data in the lower 48 states, Alaska, Hawaii, or Canada? (Each has a 'best' transformation)

Thanks,
Melita