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One thing I noticed when I looked up Ghana coordinate systems, and that led me to ask whether the first set could be overlaid over other data, is that there's a version that uses a "Gold Coast foot". It certainly looks like the layer is 1/3 the size of the other data! Leave it undefined. Add and the other data to ArcMap. Try setting the data frame's coordinate system to Accra Ghana Grid and see if they line up. You should get a gcs/datum warning message. Melita Thanks Melita, That seems to have worked! Here's the result of overlaying several shapefiles. I began with the undefined boundary shapefile (Districts), then set the data frame to Accra Ghana Grid, then added shapefiles for Africa, and then shapefiles specific to Ghana (regional, lake, airport, railroad). [ATTACH=CONFIG]26576[/ATTACH] As is, the problematic shapefile (the District boundary) remains undefined, the airport, railroad and lake shapefiles are Ghana TM and GCS Clarke 1866 with extents in meters, and the regional and Africa shapefiles are GCS WGS 1984 in dd. Thank you very much. I never would have guessed I needed to set the data frame to Accra Ghana Grid! @curtvprice - Thanks for the recommendation. @TKONG - do you think the problems you identified could cause me difficulty later on?
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08-08-2013
06:29 AM
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The 2nd extent looks very similar to the first. What happens if you redefine (not reproject) the 2nd set to use the same coordinate system? If that doesn't work. Can you overlay the first set (that's using Ghana TM) with a 3rd set of data like general country boundaries? The Ghana TM definition that you have doesn't match other definitions that I've seen for Ghana data. Melita Thanks Melita. No luck so far. Your first question: Here's what happens when I redefine the country boundary (the one with no coordinate system) using the coordinate system from the road shapefile: [ATTACH=CONFIG]26560[/ATTACH] Your second question: I didn't have a problem overlaying the set using Ghana TM with a map of West Africa I found online. This picture shows a shapefile with powerlines using 'Ghana TM'. I started with a West Africa map (GCS_WGS_1984) and had no problem adding the one using Ghana TM. [ATTACH=CONFIG]26561[/ATTACH] Where do you think this leaves me with my undefined boundary shapefile? Thanks for your help.
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08-07-2013
03:00 PM
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Hi all, I have what I hope is a simple problem from an ArcMap novice. I have two sets of shapefiles for a country. One set is shapefiles for roads and lakes within the country. The other is one shapefile for the country boundary. The set with country features (shapefiles for roads, lakes, etc) all have defined coordinate systems and overlay just fine on the fly. The country boundary does not have a defined coordinate system and that's where I'm stuck. The extent values for the country boundary are shown in this picture. From what I've read, I'm guessing the original coordinate system is projected rather than geographic (based on the size of the values). [ATTACH=CONFIG]26559[/ATTACH] I read online that one can use some trial and error and keep defining projections until you hit on the original coordinate system but I had no luck with this. If I'm right in thinking that my steps are (1) define the projection of the country boundary shapefile, and then (2) project it to overlay with the road & lake shapefiles, is there something I'm missing in order to do step 1? In case it helps, here are the details of the lake and road shapefiles. All the shapefiles (including my problematic one) come from the same office. --- Extents Top: 756142.379950 m Right: 1142656.619454 m Left: 690629.179290 m Bottom: 74790.443758 m Projected Coordinate System: Ghana TM Projection: Transverse_Mercator False_Easting: 900000.00000000 False_Northing: 50000.00000000 Central_Meridian: -1.00000000 Scale_Factor: 1.00000000 Latitude_Of_Origin: 4.66666667 Linear Unit: Meter Geographic Coordinate System: GCS_Clarke_1866 Datum: D_Clarke_1866 Prime Meridian: Greenwich Angular Unit: Degree ---- Top: 769664.186871 dd Right: 1142674.650690 dd Bottom: 57841.861131 dd Left: 650523.913583 dd Geographic Coordinate System: GCS_WGS_1984 Datum: D_WGS_1984 Prime Meridian: Greenwich Angular Unit: Degree --- Any help greatly appreciated!
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08-07-2013
01:28 PM
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