I want to measure ratial residential segregation and so I need a census tract identifier. Where can I get it?
Unfortunately, census tract information is not available in the public use microdata files due to confidentiality restrictions. You can obtain summary data at the tract level through NHGIS or American FactFinder, if that works for your purposes. Otherwise, if you need individual-level data at the census tract level then you will have to go through a Census Research Data Center. The application process to obtain such data through a Census RDC is substantial.
Hope this helps.