Suggestions needed: determining projection for old map

kfroesekfroese Geotechnical EngineerPosts: 182Trusted User
I have an old map of the Vancouver area which provides a nice grid for the city which we have been using to identify project locations in our not-very-close-to-GIS database of projects. Say, T15 tells which 10 block chunk of the city the project is in. Provides more detail than using NTS sheets.

I would like to make this map electronic but it has no projection shown. In fact, not even sure there is a date on it. It appears to be 1 5/8" to the mile scale. The horizontal grid is 1 mi, the vertical grid may be slightly less than 1 mi although that could be measurement error as I'd be surprised if the grid wasn't square but who knows.

What I did was pick a few grid intersections that lined up with road intersections to give me some reference points. I use a combination of Open Street Maps and topos in Global Mapper to identify coordinates for those locations. I then sketched out the grid in AutoCAD (trying both rectangular and square grids). I then loaded it into GM using "equirectangular" projection and then re-projected using 3 of my 4 points. The 4th did not line up nicely. Adding the 4th point into the re-projection got me errors of about 480m.

We are going to get these maps professionally scanned (they are about 36" x 48" so need to be sent out) so I will have a chance to rectify the scans and then try to generate the grid. But it would be nice to figure out the projection ahead of time and then check against the scan.

Any thoughts or suggestions on how I can proceed?

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited March 2011
    I don't know that you need to know the original projection of the data if you can get reasonably close. I would suggest maybe just using UTM with the appropriate zone, then rectifying the map image against other sources (like OpenStreetMaps data) in Global Mapper and adding enough control points (probably 5 or more) to get a reasonably accurate positioning.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
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