A popular collection in the NYPL's Lionel Pincus and Princess Firyal Map Division, and one of my personal favorites, is the county atlas series, most of which was published following the passage of a federal law commemorating the centennial of the United States. We have recently digitized 43 atlases covering New York and New Jersey from our collection of more than 420 titles printed before 1900. See this page for a list of digital holdings from this series.
Their pages are filled not only with wonderfully detailed maps on the national, state, county, township and city level, but also with interesting, flat perspective engravings depicting local business districts, prominent estates and farms. Business directories sometimes accompany the map pages that, along with the drawings, provide a glimpse into local social and economic geography of the 19th century. They also give us an idea of who provided funding for the production of these subscription based publications.