Nearly every printed topographic map I’ve ever looked at has the contour interval, otherwise known as the distance between contour lines, listed in the legend. Depending on the scale of the map, the contour interval ranges from 1 foot to hundreds of feet between each successive contour line. The contour interval allows the map reader to instantly know the relative steepness & flatness of the topography in the map at one quick glance. Because of this crucial information, a topographic map is considered incomplete when it does not disclose this information to the reader.
Enter the Terrain feature of Google Maps. Released to the public in November of 2007, the contour lines were subsequently added in April of 2008. I hadn’t really given the feature much use until last week when I was planning my weekend excursion to the Shenandoah mountains. I was trying to figure out the altitude variation on my friends property by finding where their property line started & ended and calculating the elevation change. Since their property lies on the side of a mountain, I wanted to know the altitude at the bottom of the property and the altitude of the highest portion of the property, and subtract the difference to find the total elevation variance.
What I found out instead was that Terrain function of Google Maps was lacking the contour interval declaration in the legend. As with all their maps, the lower left-hand corner showed the units of distance on the map, but was missing the topographical information provided by the contour interval declaration.
I wasn’t really expecting a response, but a couple hours later I received this response on Twitter:
Well duh. I knew that! But that is not how a topographic, err, Terrain map should operate. The user should not have to zoom all the way in, count the number of contour lines between the bold contour lines, and figure out the difference. This information should be visually presented to the user in the legend, just like how the spatial distance is shown. This is not about dumbing down the maps for users, rather, its about offering users a complete map that includes all the basic information that should be there in the first place. I responded to their tweet:
I still have yet to receive a reply…. So I have gone one step further and made some mock-up maps of how the contour interval declaration might look like.
Unlike the Satellite (and Aerial!) option on Google Maps, which allows users to zoom in as far as the imagery allows before pixillation (which is contingent on the spatial resolution of the aerial & satellite imagery), the Terrain feature has fewer zoom in levels for users to navigate. If you look closely at a URL from Google Maps, somewhere in the URL you’ll find “z=X,” where z equals Zoom (scale), and X relates to how close to the surface of the earth the map show, where a z=5 is far away and z=15 is close to the surface. The Terrain feature only shows the contour lines at 3 scales, x=13, x=14, and x=15, which means there does not need to be a complete overhaul of the Terrain maps.
Below are six Google Maps of the Continental Divide in Rocky Mountain National Park showing three different scales and how the contour interval could be shown on the maps. Of note, I am not using the bold contours as the interval, but the individual contour lines. I was able to figure out the contour interval by counting the number of intervals (5) between the bold contour lines and dividing the difference from the elevation listed on the bold contour lines.
I found this map to be the hardest to decipher the contour interval because the individual contour lines are so lightly drawn
While my use of the Geneva font with a 2 pixel white stroke might not look the best on these maps, I believe that the interface designers & programmers at Google Maps can easily implement this basic information to the legend of their Terrain maps. Yes, there will be a minor difference in the contour intervals on the maps that use meters instead of feet, but overall I don’t think it will make a large difference. The real issue is still providing users with the best & most useful maps on the internet, and until Google Maps includes this basic information, their maps will still be cartographically incomplete. The question is, will the maps be updated?