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I’m trying to georeference some old scanned maps in QGIS, but I’m not sure what CRS I should be using.

The legends on the maps say:

Numbered lines indicate the 1,000 metre Universal Transverse Mercator grid, zone 36K

Modified Clarke 1880 spheroid

WGS 84 / UTM zone 36S (EPSG:32736) seems to be giving me the best results, but it’s still not satisfactory. See particularly the tile overlaps and streams in the image below. If I choose WGS 83 (EPSG:4326) my georeferenced images disappear from view.

I’ve been using “Linear” for the transformation type and the resampling method in the georeferencer. Might it help to use other settings here?

Georeferenced image poor alignment

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    hell thats an old spheroid...check if the 'new arc 1960' elipsoid fits your needs (EPSG 21096, for UTM 36N or EPSG 21036 for UTM 36S, both nat. crs for Kenya)
    – geozelot
    Aug 1, 2017 at 21:38
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    It's in Mozambique, not Kenya. Try 2736, Tete / UTM zone 36 South although Tete is based on Clarke 1866. The modified Clarke 1880 makes me think of South Africa and the Cape or possibly Arc 1950 datums.
    – mkennedy
    Aug 2, 2017 at 2:51
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    You might try thin plate spline instead of linear, together with EPSG:2736.
    – AndreJ
    Aug 2, 2017 at 5:51

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Thanks for the suggestions. I tried thin plate spline transformation and EPSG:2736, and got much better results. It’s still not perfect, but close enough for my needs. I tried that CRS before, but with the thin plate spline it gives much better tile overlap, and the offset seems to be smaller.

The region is along the border between Zimbabwe and Mozambique. It’s slightly complicated by the fact that the scanned sections were trimmed from the full sheets, and I don’t actually have any accompanying information for those. I do, however, have a full sheet for the next section to the east, and that’s where I got the information above. I’m assuming that the CRS is consistent across the set. The scans above use metres for elevation, however, and the full sheet I have uses “Heights in English Feet based on Beitbridge Datum”, which makes me think that the publication dates are different.

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