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I have some scanned paper topographic maps of Comoros with the following projection information: Comoros projection info

I believe that this corresponds to EPSG:2999. However, after getting good control points in the QGIS georeferencer and reprojecting to EPSG:4326, the maps are consistently offset by a little over a kilometer to the northwest when compared to Google satellite imagery. Any thoughts on where to look for the culprit?

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  • Check the Datum on your control points.
    – Pointdump
    Commented Oct 20 at 9:29

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There's a Grand Comoros geographic coordinate reference system (CRS), EPSG::4646, in the EPSG dataset that EPSG::2999 (Grand Comoros / UTM 38 South is based upon. There's also a coordinate operation (transformation) between Grand Comoros and WGS84, EPSG::5521, which has relatively large XYZ offsets: -963.0, 510.0, -359.0. The accuracy of the transformation is uknown.

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