The New York Public Library Public Domain Documents page is http://www.nypl.org/research/collections/digital-collections/public-domain:
Searching for "maps" brings up this page - http://digitalcollections.nypl.org/search/index?utf8=%E2%9C%93&keywords=map&filters%5Brights%5D=pd#
I reviewed a number of them, and picked an 1843 map of the entire state (with an inset of New York City).
I could zoom in only a bit on the online map, but further down the screen is information for the map and the green buttons to download the map for a range of dots per inch:
I chose the "Original" button, and downloaded the 1843 map to my computer. It was 5,699 kb.
I then opened the map image with my Photo program, and was able to zoom in quite far before it lost resolution. Here is a screen shot of Erie County:
There are a lot of historical maps on the site, and many maps of New York City from colonial to modern times.
This is a tremendous website, and a real boon to New York researchers like me. I did not find any cadastral maps of the counties, which may have farm owner names in each section or town, but I may have missed them in my review of the site.