Annual median $/SF is the typical price per square foot for homes that closed in the ZIP code over the twelve months ending on the date in the heading: half sold for more per square foot and half for less. Last year is the same figure for the twelve months before that, so comparing the two columns shows how much prices per square foot have changed.
ARMLS closings is how many homes sold in the ZIP code over those twelve months. The median $/SF beside it is worked out from those sales, so the more closings, the more reliable the figure. A ZIP code only appears once it has at least 20 closings in the period. Hover over a ZIP code to see how many it had the year before. Tap a ZIP code to see how many it had the year before.