# How do I determine the projection of a paper map?

If I'm reading a paper map how do I determine what projection was used to draw the map if such information is not explicitly labelled on the document?

Online it is easy to find resources (for example, Wikipedia or GIS Wiki) that describe and classify the various projections in use. However, as a non-expert map user I find it difficult to use the construction details in reverse, to determine what projection has been used to draw a particular map. I thought perhaps there might be a flow chart or other classification process that could help a map user determine the projection in use?

For example, at my local library and archives there is a copy of a map lithograph from the Dominion Lands Office (Canada) dated 1878. The map has curved parallels and meridians that are wider at the bottom than the top (the top being closer to the pole in this case). I think this makes the map a conical projection, but I'm not sure. And, if that is correct I am interested in learning if it is possible to classify the projection more precisely (e.g. Lambert conformal).

I have made a partial scan of this 1878 map (it is too large to scan the whole thing with the equipment I have available) in case that helps anyone answer my question.

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Conformal projections with graticules are easy to spot: the meridians and lines of latitude will always meet exactly at right angles. The exact shapes of the curves can help in narrowing down the possible projection, so posting some scans would still be a good idea. – whuber Mar 30 '12 at 20:28

A good source of information is http://www.asprs.org/persjournals/PE-RS-Journals/Grids-Datums.html (Grids & Datums by Clifford J. Mugnier). In 1997 a paper about Canada was published, perhaps it gives some insights.

Otherwise, post your question on this mailing list (where also C Mugnier is reading):

http://lists.maptools.org/mailman/listinfo/proj

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Mugnier is the authority on datums around the world. – whuber Mar 30 '12 at 14:28

I've never used it before but I suppose Blue Marble's Projection Recovery Tool might do this.

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