OpenStreetMap is to crowdsourced geospatial data what Wikipedia is to crowdsourced encyclopedic articles. OSM is also a community of GIS user who are active in mapping the world’s geographic features (roads, rivers, boundaries, hospitals, schools etc) and will mobilize whenever disaster strikes (ex: West African Ebola outbreak).
OSM data search and download: overpass turbo
Feeling lost with OSM, like its features syntax? OSM Wiki
General geographic data
DIVA-GIS is your source for shapefiles at the national level of simple map features like vector roads, railroads, and water features; and elevation and population raster dataset. The data was compiled by a collaboration between several institutes and the University of California.
Infrastructure Africa, managed under the African Development Bank Group, provides shapefile format infrastructure data which include roads, power line networks, and power plants. I personally find the road data to be more complete and accurate in OSM.
Columbia University’s SEDAC provides raster, tabular (csv) and vector shapefile data on population, climate, and other various thematic sources pertaining to development and agriculture.
U.S. Census Bureau’s TIGER for census block and demographic population datasets in the United States and its territories.
From the makers of DIVA: WorldClim. Contains a set of climate layers for current conditions (1950-2000), future prediction (according to the IPCC5’s report models); variables included are monthly minimum/maximum temperature, precipitation, and ‘bioclimatic’ variables.
New York City metropolitan data
The Metropolitan Waterfront Alliance lists sites relating a variety of GIS data for the New York City metro area.
More New York metropolitan area data from the University of Columbia’s digital service center.
Oasis NYC hosts and lists various metro data ranging from subway routes, land use, and an assortment of demographic data.