The HathiTrust Digital Library brings together the immense collections of partner institutions in digital form. Hundreds of full-text historical guidebooks about New York City and the Boroughs can be found by search the digital library. To search the catalog, go to the advanced search screen and search "guidebooks" and "name of place" in "Full Text and All Fields" and limit to English. For example:
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"These volumes comprise New York's official 'Master Plan,' enormous and far-reaching in scope but designed for the speediest possible implementation. the proposals of the plan have caused much controversy and even disruption since their first public presentation in November 1969. Reactions have ranged from high praise as 'a strong and extremely significant document' to charges of being 'merely a listing of problems rather than solutions'." - Description from Alibris.com
This six-volume set's index and chronology (volumes four, five, and six) are especially valuable. "This reference book records important daily events taken from contemporary sources, like newspapers, and features an index that includes information about land grants and farms, entries for streets, buildings, and individuals, and much more from the history of the island."