Spent some time today trying to display a historical aerial photo in a map context. Here’s some notes on using QGIS and Felt.
Someone told me about UCSB’s aerial image archive. It’s remarkable: a large collection of historical aerial photographs, many free of charge. All georeferenced on a tool called FrameFinder and easily downloadable. So I found one from 1952 that covers the area my house is in and wanted to put it on a map. Not too hard but not easy.
Georeferencing
The FrameFinder images aren’t GeoTIFFs, they have no spatial data. So first I used the QGIS georeferencer to get them on a map. The source images are very nicely scanned and taken, I suspect they are true straight down images. Even so I put down about 12 control points on road intersections by reference to Google Satellite imagery. Then I used the Projective transform to warp it; it ended up slightly angling the source image. Important to set the “transparency is 0” option so the border of the warped image doesn’t obscure things!
I wish the QGIS georeferencer were more nicely interactive.
QGIS
With the image georeferenced it was very simple to load it as a layer in a QGIS map. I tried a bunch of different ideas for a base map to reference to. I finally settled on MapTiler’s plugin, their Toner layer is a nicely styled vector map that you can plop on top of a raster image like mine. I customized the symbols: removing most of the polygon fills, turning rivers blue, etc. The result looks OK.
The other thing I did was use the Google Satellite layer in the background. Normally it’s obscured entirely by the older aerial photo but you can easily toggle that off and on to do a quick before-and-now comparison.
An aside: every time I do something new in QGIS I start by just hacking something up loading data from any-old-place, often my browser Downloads folder. Then I have to do extra work to rebuild the project with the files in a permanent place. Would be better to always put all the assets in one place first before working with QGIS.
Felt
I also gave Felt a try, a nice mapping startup. They have a really great tool that makes it easy to make custom maps with some light GIS work and styling. Drop a GeoTIFF on the map, select Roads and Buildings as vector layers on top, and you’re basically done.
Hit a bummer though: everything was looking good and I was ready to share it, then I reloaded and got a big “Paid plan required” overlay. I had hoped something this simple would be in the purview of their free plan but I think maybe adding a single custom image like mine puts me over. Felt a bit like a bait-and-switch, it letting me work for an hour+ before learning I’d have to pay. Not sure this one map is worth paying $30/mo to share but I have a bigger project in mind that would warrant the expense. Felt’s product is really nice and it’s all so fast!
MapWarper
For a third shot I made a version in Map Warper. This worked great. The control point UI in the rectifier is very nice and easy to use. The whole site is so tight, really easy. And there’s a nice preview mode with a simple transparency slider. The site is more of a tool for rectifying TIFFs, I think it’d be neat if it were enhanced to be more of a publishing site itself. That’d imply some hosting and serving costs though.
Something custom?
I feel like there’s room for a very simple “before and after” map webapp that takes a GeoTIFF and displays it against a basemap. With a toggle or slider or lens or something to let you see the old image and what it looks like now. I could probably cobble up something basic in a few hours. Hosting the GeoTIFF is the hard part although if you don’t bother to cut it into tiles it’s not too much. The closest I’ve found is GeoTIFF.io.
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