I am trying to use modern USGS DEM data with older USGS maps. The first step, as far as I am aware, is to reproject the contemporary DEM into the same projection as the old USGS map. The old USGS map notes that it's a "polyconic projection. 1927 North American Datum. 10,000-foot grid based on Oregon coordinate system, north zone."

Based off of some sources I found online, I need to define the projection using a proj code. A little more online digging yielded this: "+proj=poly +lat_0=0 +lon_0=-122.625 +x_0=0 +y_0=0 +a=6377397.16 +b=6356078.96 +units=m +no_defs". I tried using this with gdalwarp, as follows: gdalwarp -t_srs "+proj=poly +lat_0=0 +lon_0=-122.625 +x_0=0 +y_0=0 +a=6377397.16 +b=6356078.96 +units=m +no_defs" -r bilinear -of GTiff -co "TFW=YES" dem-edit.tif dem-edit-2-5.tif

The final image generated appears rotated, both if I open the TIF directly, and if I open it in QGIS. New tif

New Tif opened in QGIS

My intuition is that this is something to do with the projection I defined.

Does anyone know how to correctly use American Polyconic, NAD 1927 with GDAL and CLI also QGIS?

It seems that theres no EPSG code, and my best guess is that there's something wrong with the proj code.

Ultimately I plan to load the DEM and the old map into Blender for some 3D renderings, so if there is another projection that would give me close enough results to the original then that could probably work as well. In the GDAL command instead of defining a and b, I also tried +ellps =clrk66 to no avail.


1 Answer 1


I stumbled upon this post with a similar issue (same reference to NAD27 Polyconic on an old 1950's soil survey, different state). However, I believe I've come across a solution.

The USGS Historical Topo Map Collection has a viewer with, as the name implies, old historical topo maps. Viewer is located here https://ngmdb.usgs.gov/topoview/viewer/. Each topo map has been georeferenced. For the particular one I was looking at, it has the same NAD 27 Polyconic Projection I needed to reference the map I was working on

Map Details

When I downloaded it and added it to ArcGIS Pro, it verifies the correct projection, and I'm able to reference that projection for my data frame. Hopefully something similar is possible for QGIS/GDAL.

enter image description here

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