(Resending, with screenshots as google drive links, to cut down message size.)
I am running 3.12.1-București on a mac, os-x 10.14.6. My knowledge of GIS is rudimentary, I've learned what I need to, to satisfy my curiosity about my region, using old maps. I have downloaded all the USGS maps for my region - Oakland, CA, USA, which corresponds to "CA Concord" - from USGS topoView, in geotiff format. Opening them in QGIS gives fairly wild offsets; they are not all encoded the same way, yet have common corners. Features on the map vary with what modern maps show, but getting their corners right would help me a lot. If I create a new project, set my CRS to WGS 84 / Pseudo-Mercator (EPSG:3857) as I think is correct for my base map, Google Maps (EPSG:3857 - WGS 84 / Pseudo-Mercator - Projected) then Layer > Add Layer > Add Raster Layer > Raster Dataset > CA_Concord_465520_1943_62500_geo.tif > Add, I get prompted with: https://drive.google.com/file/d/1FKVPrHLtXXKK8a-QTTz3IigT9dpj1Hou/view?usp=sharing I don't know what to choose, here. I chose the first one. I've tried others. The tif.prj file does say DATUM["D_North_American_1927",SPHEROID["Clarke_1866",6378206.4,294.9786982]], which I am guessing conforms to NAD27. If I add an opacity slider to the new raster layer, set its opacity, and then use the Zoom to Coordinate panel to navigate to 37º45'N 122º15'W, I find that the point is off from what's on the map, see: https://drive.google.com/file/d/10vYtcM1FZ-vdS3z1FPW2EYbrNy2sj65L/view?usp=sharing This is similarly true at the top left: https://drive.google.com/file/d/18naBKuwk6rZ9DP0tFOZxnGKlIpRQgDKM/view?usp=sharing Also, note how the map shows two lines at top left, it's true at top right. This is something to do with projection, I think. I've tried to georeference these lines, to get them to line up right, but which intersection do I use, when there are two vertical lines intersecting with the top, horizontal border, to reference 122º 15' 38º 00' ? I've had mixed results, trying to use deg-min-ss coordinates to georeference these; I get a map off the west coast of Africa. Using points on the map is more successful. All the maps have slightly variant values in their tfw files. Their prj files are more uniform, but also show variations. I'd like to normalize them all, so that I can view the USGS topo maps for my region over time. Advice? Thanks, Morgan
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