I was searching today for directions to one of my daughter's friend's house. Of course, I just typed the address into the search bar and up it came in Google Maps. However, the hybrid view, with major streets identified on top of satellite imagery, showed discrepancies. The overlay drawing of the streets at one important intersection did not line up with the roads in the picture. Which was correct? Naturally, I would just assume that the picture is out-of-date, as it is easier to update a map than a satellite image. But, as a geek, I wanted to prove which was correct.

Two Watches

There is an old saying that "a man with one watch always knows what time it is, while a man with two watches is never exactly sure". I've always liked that adage, but I've learned through puzzled looks that some people don't find it meaningful. The point is that two watches will generally tell you two different times, and you will always be unsure of the real time by the difference between the times on each.

In this mapping case, a second "watch" would come in handy to check the accuracy of the first. That second source would be Yahoo Maps.

The discrepancy occurs (at least today - it may be updated before you read this) at latitude = 39.181506 and longitude = -76.899603. For Google Maps, type "39.181506, -76.899603" into the search bar. You should see the discrepancy where the drawing of "Pindell School Rd" goes across an open field. If not, the imagery may have been updated. I have included a screen capture as the image at the top of this page (click to see it full res).

Here is a link to the same spot in Yahoo Maps. Notice that the map drawing is the same, but the satellite imagery is different. The satellite matches the map drawing. More evidence that the map drawing is correct, as I suspected.

Ch-ch-ch-changes

Unfortunately, I was intrigued. What else had changed between the satellite images? And could I prove which one was more recent? After all, the change in the roadway seemed to make things more complex, not less. If Pindell School Rd got lots of traffic, engineers would prefer the Google image road layout over the one in the Yahoo image. On the other hand, if Sanner Rd got more traffic, then the Yahoo image road layout would be preferred.

Besides, I was just curious. I'm a researcher. Finding things out is what I do.

The most obvious thing would be new construction. If I could find new buildings in one satellite image that were not in the other, I'd have my answer. This part of Howard County was mostly built out a couple decades ago, but there is still plenty of new construction going on.

In searching the nearby subdivisions, nothing caught my eye. I did find a parking lot at latitude = 39.174628 and longitude = -76.851097 that seemed newer in the Yahoo image. However, the Google image was fuzzy and the comparison didn't convince me.

Continuing to search, I eventually found a definite difference. It occurs (at least today) at latitude 39.16913 and longitude -76.864761. Here is the link for Yahoo Maps. For Google Maps, type "39.16913, -76.864761" into the search bar. Zoom way in and you will see three buildings below and left of center that exist in the Yahoo satellite image, but not in the Google satellite image. Assuming that construction prevails over destruction, Yahoo has the more recent image and should be trusted for the directions.

Waldo?

Now this exercise was mostly academic, since my natural assumption was to trust the map drawing over the satellite in the first place. But still, it was kind of fun to scroll the two map services side-by-side looking for differences. Sort of a real world "Where's Waldo?".

It is the kind of thing my mind enjoys, with just enough real world justification to rationalize the endeavor. Try it. See what difference you can find in your neck of the woods. That new shopping center at Quarry Lake - I wonder if either of them has that mapped out yet ...