GMZD: Google Maps Zoom-out Distance
Here’s a fun and simple measure of distance between any two locations, A and B. First, find A using Google maps and zoom in (centered) as far as you can go, though don’t go into street view as lots of places still don’t have that. Now, if you can already see B on the map, it has a Google Maps Zoom-out Distance (GMZD) of zero because you don’t need to zoom out at all to see B. If you have to zoom out once, then A and B are at distance 1 according to GMZD, etc.
For example, let’s start with Union Square in New York. Fully zoomed in we can see Coffee Shop, so that’s at distance 0. Those things are about a minute’s walk from the center of Union Square. Zooming out one click, we pick up Bowlmor Lanes on University Place and the Whole Foods Market at the South of Union Square. Those things are at GMZD-1. The outer edge of distance 1 is about a few minute’s walk from Union Square. Continuing outwards, Betaworks is at GMZD-4, Central Park at distance 6, Boston and Niagara Falls at distance 12, Florida, Winnipeg, and St John’s, Newfoundland at 14, San Francisco at 15, Barcelona at 16, and Sydney at 17. (Although you can zoom out 18 levels, GMZD-17 seems to be as many as you practically need to see anything.)
You can also think of GMZD as half the number of clicks you’d need to do on Google maps to go from being fully zoomed in on A to being fully zoomed in on B (with some panning in between). When you look at Google maps you can count the number of notches on the little slider (see image on left) above your current zoom level to see the GMZD from the center of the visible map to its outer edges.
Update: I meant to mention that GMZD is not a formal distance metric. It is non-negative (GMZD(A, B) >= 0) and symmetric (GMZD(A, B) = GMZD(B, A)) for all points A and B, but distinct points can be at distance zero and (as a result) the triangle inequality also does not hold (e.g., Union Square is distance zero from Coffee Shop, and Coffee Shop is distance zero from Union Square Cafe, but the distance from Union Square to Union Square Cafe is one. Not being a metric space is what makes it interesting, though :-)