Using Geo Mapping

Hi,

I've been able to get Zoho Reports to generate some geo maps but am having some issues with 'unresolved' location. I currently have the United States Postal Service Zip Code data set loaded. I use that to 'tag' all geo columns onto my data. It doesn't seem to be working 100%. What geodata should I be using to get it to work accurately. I've attached the sample map I'm working on with the data I'm missing.

In this example I'm missing Jackson County, Oregon. I know there is a Jackson County in several states but my tables do include zip code, city and state.

Can I download the data set to tag to my data and where can I do this?