Syndicate plat mapping, an example

[jrbouldin]

I currently have around 150 original township plat maps, dating mostly to the 1880s, that I have geo-referenced and rectified.* These steps are necessary to allow overlay on modern digital layers such as USGS hydrologic layers and DEMs. Google Earth is a very useful tool in this process, in that it will easily drape the plat over its landscape imagery, giving a 3-D effect, and the map doesn't even have to be in the same projection as the imagery. Nevertheless, I'm not satisfied that I've found the optimal method of displaying these maps and the many large and small errors of all kinds contained in them, relative to the actual landscape.

Here's one example, from twp T01NR21E MDM, which is in the heart of Yosemite NP, just E of the main body of Hetch Hetchy Reservoir. The principal topographic feature of this township is the Tuolumne River, including parts of the Tuolumne Canyon. This township was "surveyed" by Solon A. Hanson, one of John Benson's most prolific producers of garbage but who mostly escaped scrutiny and indictment due strictly to fortunate timing. This twp was part of an enormous Hanson contract that covered areas now in Yosemite and in the Stanislaus and Humboldt-Toiyabe National Forests. Being in Township 1 North, it's southern boundary is therefore part of the Mount Diablo Baseline. In theory.**

There are three linked images.
The first one is just an oblique aerial view looking a little N of W, across the landscape. The blue lines are the USGS stream layer, clipped to the twp boundary and thus containing numerous detached fragments. [The apparent widening of the Tuolumne is actually the upper reaches of the flatwater of Hetch Hetchy Reservoir.]
(1) https://drive.google.com/file/d/1pb1nTS ... drive_link

The second one is from the identical position, but now including the twp plat map draped over the topography, and indicating the position of the mapped, versus actual, course of the Tuolumne River.
(2) https://drive.google.com/file/d/1gNZrHt ... drive_link

The third is a view from roughly the opposite direction and on the opposite (western) side of the twp, intended to show that portion of the Tuolumne River mapping error.
(3) https://drive.google.com/file/d/10toMDG ... drive_link

There are all kinds of errors on this map, major and minor. In fact, except for the general westward course of the Tuolumne, almost nothing is accurate in any way. The Tuolumne is mapped as running for several miles along the side of its canyon wall, including uphill for long distances. The E and W twp line crossings are off by 3/4 to 1 full mile, and the midpoint in Section 28 by about the same. Other tributaries also sidehill, as well as crossing ridges and merging with completely wrong or non-existent other branches; ridgelines are depicted in canyon bottoms (Secs 26, 27); nonexistent peaks are scattered throughout; moderate slopes are labeled "canyon" (Sec 2); etc. At best, Hanson did nothing but draw the map based on views from local high points, most likely from the elevated table land south of the river. Almost none of the depicted stream or ridgeline crossings of section or twp lines match reality.

And this is by no means the worst Syndicate example, or even the worst Hanson example.

* That very important process is a bit of a story that I don't have time for at the moment, but maybe later. To make a long story short, I pinned the twp corners to the coordinates given in the CadNSDI (formerly GCDB) database using two predictive equations for error correction, interpolated across the map image.
** The survey of the MDB is a weird but very interesting story in itself, but again, maybe later.