IFR/VFR Weather Question?

Got a question, hopefully someone can clarify my confusion. At a Cl D airport the ceiling was 800ft and IMC, then the next hour it was 1100ft and VMC. I thought in Cl D the VFR mins are 500ft below the clouds and the minimum safe altitude over terrain is 1000ft so therefore it has to be 1500ft to be VMC but if I remember I don't not recall seeing anything like this in the FAR's. Unless the minimum safe altitude is 500ft at this airport because it's not as congested then that makes sense. I guess my question is what are the minimums for the ceiling in Cl D for it to be VFR, does it depend on what the terrain is clified as around the airport (i.e. congested, other than congested)?