[Qgis-user] Aligning georeferenced USGS historical map

[Andre Joost]

Am 16.11.18 um 14:36 schrieb Andreas Plesch:
> Looking at
>
> https://ngmdb.usgs.gov/img4/ht_icons/Browse/CA/CA_Tamalpais_301790_1897_62500.jpg
>
>  there is a note in the lower right corner:
>
> Polyconic projection. To place on North American datum, move
> projection lines 690 ft south and 320 ft west.
>
> https://en.m.wikipedia.org/wiki/American_polyconic_projection
>
> explains the projection.
>
> Unfortunately, the map does not mention which central meridian was
> chosen for the projection. It may be possible to find if at the time
> a single one was used for all of CA and what it would be.
>

Maybe related: 
https://www.usgs.gov/faqs/why-are-historic-maps-referenced-outdated-datums

Following that, the central meridian of the polyconic projection goes 
through the center of the map quadrangle.

HTH,
Andre Joost