Most of the resources listed in this guide provide geospatial data and are in the public domain. The data has been collected and distributed intentionally for use in GIS applications. There is a lot more data freely available from many sources that can be used in a GIS. But in order to use it you must be able to join it to the geopsatial data. If you find crime statistics is there a geographic identifier associated with the data? If it is a table of data points does it have an "x" and a "y" value for each row? If the data applies to an area such as a state, county or census tract does it have a "FIPS" code or an identifier that can be translated to the Census Bureau's codes? Without having a geographic identifier it may not be possible join the tabular data with the spatial data.
Does location matter to your research? Is it necessary, for example, to display mortality rates on a map of New York State? If the rates are higher near a toxic dump site, it may be. If the rates are organized by congressional district, it may not. It is important to think about these issues from the very beginning of your project. What geographic domain makes sense? Where can I find data that is geo-referenced to that domain? How do I join the tabular data with the spatial data in a GIS? What symbology is appropriate for the display?
Some other considerations when using spatial data in a GIS:
Is the data in the proper format for its intended use, i.e., Shapefile (.shp) or Geodatabase (.gdb) for ArcGIS, (.kml) for Google Earth?
Is there a projection associated with the data? Does it match the rest of your project?
Is there a scale? Does it match?
for tabular data:
At what level is the data aggregated? Is it by individual, household, census tract, county?
Is your data consistent in the way it was collected and represented? Data from one source may be weighted, others may not be.
How recent is the data?
Is the data in the public domain? Is there copyright?
Enter your search term, e.g., New York to find GIS data on the web for New York State
Portals provide a user interface and a service for searching across data domains.