"Click on the Latitude field and drag a copy next to itself in the Rows field. This will create an identical map on the same sheet as follows." —- You have to hold down the Ctrl key to copy!!

I noticed this too. The reason is because the visualization assumes your GPS location is the United States!

I am living in Japan and doing this tutorial, so it assumed that the postal codes were in Japan and couldn't find them.

If you notice, there should be a little message in the bottom right-hand corner that says "631 unknown": "631 values that have unknown geographic locations," etc. That was my first hint.

If you just drag the "Country" dimension to the "Marks" panel, all the dots will show up on the map.