Are there any mapping programs which show property values?

[Bob Jones]

This is a bit of a newbie question. I assume there must be color coded maps which let you see property values at a glance. But, I'm having trouble finding this online.

I'm not sure if there are any mapping programs which show you the entire nation, or if you need to search for maps specific to your part of the country. If the later is the case, I'm trying to find a map of home values in Baltimore City and Baltimore County. Can anyone offer any advice?