Since I only have Incorporated area feature class, how can I select census blocks that are in unincorporated area? Or not within any incorporated areas?
Select by Location, in Arcinfo, will give you a variety of options to refine that requirement.
Give this a shot:
To read more about this check out this link from ESRI Help: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Select_Layer_By_Attribute/001700000071000000/