July 31, 2026

The QGIS program - Topo maps - Part 1 - sources

There are a variety of ways to pull these in as a layer. He pulls in a scanned quad map that he has as a PDF. He uses Raster -- Georeference from up top. My version does not have this. This video is 7 years old -- so let's try another. He uses OSM standard from Quick map services plugin, then picks points on this map that he can also reliably find on the map he is working with. Use the Web dropdown menu to get to the plugin. The menu has been rearranged since his time, but I can browse around to find OSM standard. This gives me a world map on the screen that I can zoom in on, and pretty soon I am looking at the Mt. Wrightson area in the Santa Rita Mountains south of Tucson.

I follow his example and install the OSM place search plugin and once it is installed, I can get to it from the Plugins drop down. I can search for Wrightson and Tombstone with sucess and zoom there, but other things I try are apparently not in its database.

I decide to work with the "Fagan" PDF I have. I pull it in as a layer, but since it is not georeferenced, who knows where QGIS locates it. It certainly doesn't show up.

Now use the Layer dropdown and select Georeferencer. At the top left is a blue square that is "open raster". I use this to browse my way to the fagan.pdf and indeed it appears in the georeferencer canvas. I click the "hand" icon in the toolbar and I can drag the image around and zoom on it. I need to switch from this to the "add point" mode, which yields a crosshair icon.

I go to the upper left corner of the map, which is nicely marked with lat and long for me. The video shows him using the "From Map Canvas" in his case, as he can find a nice landmark on both maps. Note that longitude does enter as a negative value. I type the values in as dd mm s.s This is called a GCP (ground control point). He adds 10 points. He next fiddles with tranformation settings, which lets you choose from a menu of algorithms. He uses Polynomial 1 and leaves the Target CRS as EPSG:3857, which is his project CRS.

I enter 4 points (the marked corners of the quad) and leave the algorithm set to linear. It selects "fagan_map_modified.tif" as an output file with nearest neighbor for a resampling algorithm. I click OK on the settings then use the green triangle to run the georeferencing. I see the new layer pop up in my layers list, but nothing on the map. I can right click on the layer and then use "zoom to layer" to see it. I right click and use "properties" and "source" and see EPSG:3857 I see the same thing for the OSM standard layer.

When I look at coordinates for my georeferenced map, I see long, lat values like -110, 32. But the OSM map show big integer values, which are meters. Both claim to be using EPSG:3857. I read that EPSG:3857 uses meters. So I change the CRS for my georeferenced Fagan map to EPSG:4326 and that seems to do the trick.

Indeed the two maps now seem to be properly aligned. But the OSM map has virtually no topography. We need something else for that layer.

I save this project as "fagan1".

USGS topos

Find "XYZ Tiles" on the left, right click and select new connection.
Enter: 
Name -- USGS Topos
URL: https://basemap.nationalmap.gov/arcgis/rest/services/USGSTopo/MapServer/tile/{z}/{y}/{x}
I double click this to add it as a layer. It is nice, but it is not the old 15 or 7.5 minute quads. I do not see "Cuprite Mine" labeled as an important example.

more on Topo maps

I launch this.
I zoom into the area I want.
I select US Topo and select both current and non-current.
Then I click on "Search Products" towards the upper left.

The results include the Mount Fagan 7.5 minute map. I click on the "Download Link (PDF)" and I get the following 47M file: 

AZ_Mount_Fagan_20210901_TM_geo.pdf
I move it to /home/tom/qgis and drag it to my layers list. It gives me almost a dozen layers. But none show the mine names I am itching to have! This is cute (too cute). What I want is a scan of the original USGS quad sheet.

I launch the TopoView app. I can just type in "Mount Fagan" and it find two. The first one is in Arizona and is the one I want. Once I click on it, it shows me various 1:24000 maps (7.5 quads), but also the 1:62500 15 minute quad from 1958!! Also a Patagonia 1:125000 sheet from 1905 and a Nogales 1:250000 sheet from 1956.

There is a 1981 and a 2018 edition of the Mount Fagan quad. I download the 1981 as a GeoTiff. This is what I want! It is a raw scan of the original sheet with borders (not georeferenced) and includes mine names.

Feedback? Questions? Drop me a line!

Tom's Geology Info / tom@mmto.org