Jeff it does sound as if you are missing some postal codes in your data (or Tableau is). Here in the US, ZIP codes change a lot (USPS estimates about 25,000 changes per month.) So it's sometimes difficult to get everything to match up. When this happens to me I turn on the ZIP code labels on the underlying map and start adding the ones that are in the blank area to my data set. Eventually I usually find all the ones I need to fill in the map.
What format would the postal codes be in? For example I normally will see the postal code like the following,
This displays a space in the middle.
but I have also seen them with out the space. I'm assuming it Tableau listed the postal codes with the space I would have to follow the suit?
I believe that will actually work out better. it will allow more area to be covered which is what i truely want. now i will have to figure out if it will work. thanks
As Shawn indicates, they do only use the first three characters in the postal code.
Tableau does not, however, go down to the county level.