Esri Mapping Center - Ask a Cartographer

Digitization

July 29 2010 | 2 comments
Categories: Map Data

I am a beginner in ArcGIS, and I am using ArcGIS 9.2.

I uploaded a raster data, registered it and set the datum as WGS_84. For digitizing some points over this data I have also created a shapefile with the data fixed as WGS_84, but while digitizing it is warning me that the co-ordinate system are not same, that may be causing an error.

Please solve me this problem

Mapping Center Answer:

When you first added the raster image to ArcMap and registered it -- how did you do that? Did you add another file to the ArcMap session that you knew was in WGS_84 and then register the raster image to that? If so, then double check that the file you used to register the raster image really is in WGS_84.

If instead you added the raster image to ArcMap and used the Define Projection tool to simply define the raster as WGS_84, then you missed the step of registering the image to a file with the known WGS_84 projection. Simply defining it as WGS_84 does not actually make it WGS_84 if it really was not in the projection to start with.

Therefore, you need to check two things: 1) that the image you registered REALLY is in WGS_84 and 2) that the shapefile you want to create is defined to have the WGS_84 projection. If you take care of this and still have the problem, please get back in touch with us and we will try to help you further.

Please suggest the projection I should use for Mer posted by Faizal KV on Jul 30 2010 3:53AM

The map I want to digitize is produced in the Mercator projection by Generic Mapping Tool (GMT). I first clicked "Add Data" and added the data, then I registered it. Then from ArcCatalog I have given the geographic reference as WGS 84. (Now here I have a doubt -- which coordinate system should I can give for the Mercator Projection)? Then I created a shapefile and gave it WGS 84. And then I started editing. Now I am also facing the same problem. It warns me that both the layers are in different coordinate systems and an error may occur.

A little more info posted by Aileen Buckley on Jul 30 2010 9:14AM

Can you please send us the exact projection specification from the GMT output? This would be something like the following:

World_Mercator
Projection: Mercator
False_Easting: 0.000000
False_Northing: 0.000000
Central_Meridian: 0.000000
Standard_Parallel_1: 0.000000
Linear Unit: Meter

GCS_WGS_1984
Datum: D_WGS_1984

Name: GCS_WGS_1984
Angular Unit: Degree (0.017453292519943299)
Prime Meridian: Greenwich (0.000000000000000000)
Datum: D_WGS_1984
Spheroid: WGS_1984
Semimajor Axis: 6378137.000000000000000000
Semiminor Axis: 6356752.314245179300000000
Inverse Flattening: 298.257223563000030000

The more info we can get about the projection, the better able we will be to help you! :-)

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