Thoughts - Lost in DCW, Togo and Off on a Tangent
Togo Country Map
For the past 3-days I've been lost in the world of DCW - Digital Chart of the World (aka VMAP). I know more about this grand mapping monument than I should ever know. It is based on ONC 1:1,000,000 scale military base maps that are based on some pretty old data (WW II and beyond). The ONCs were constructed for pilots to scan the earth as they are flying for identifiable features. ESRI took these maps, back in the early 1990s, and digitized them. From this data they created the Digital Chart of the World. Now let's fast forward to today.
I am currently teaching 6th graders about African geography. The region of Africa that is always a challenge is West Africa - Ivory Coast, Ghana, Togo and Benin. So I dutifully teach them and they dutifully learn all about African countries. In the process, curious soul that I am, I decided to study the available mapping of a small African country - Togo. One of my favorite mapping websites is Relief Web, a UN affiliated group that reports on people in need and helps to coordinate relief efforts, thus the name. They have a mapping library that is very interesting. So I wandered into their map library and snagged a few Togo country maps - one produced by the CIA (the bland one) and the other produced by the French government (the colorful one). The CIA map is a relatively old map, but the French product claims to be produced in 2006.
Curious soul that I am, I load the French map into Global Mapper, georectify it and digitize the road network for Togo. It didn't take long, maybe an hour. I imported this Togo road network into Marplot and compared it to the DCW Togo road network. You know the answer - it was the same road network, the DCW stuff.
And than it hit me. Almost every small scale base map found today still uses DCW layers of information. Some of these layers (elevation, rivers, etc.) will always be useful. Some of the layers, like roads, were poorly plotted on the ONCs originally and the same misplots are still being used today. Just overlay DCW roads on top of the appropriate Landsat ETM+ imagery and you will see DCW roads seldom, if ever, match the actual roads. Landsat ETM+ could be used to correct some of these transportation misplots, but it is tough to do at it's typical pixel resolution. The 1-meter resolution imagery is the ticket! (Are you listening Digital Globe?) I know it is being used to create up-to-date road maps in large cities, but it should be used to create the NEW and IMPROVED DCW. What a cartographic coup for the entreprenurial company (Are you listening Digital Globe?) that would sponser this effort!
And that was my tangent! What the heck am I messing around with Togo road networks and DCW when I want to make maps of islands. For 3-days I've been lost in DCW, Togo and off on a tangent. Oh, well, perhaps this evening I'll get back to my primary mission, island mapping, and leave my DCW / Togo tangent alone.
A word of warning - Tangents are alluring, but typically take you where you need not go. Stick to your target path. It's where you want to go.
Enjoy!
Labels: DCW, Digital Globe, ESRI, Global Mapper, Marplot, Relief Web, tangents, Togo
