I like the connection between elevation and negative numbers. Perhaps I could also work in a social justice element by examining flood and elevation maps.
Animation of Katrina Flood via NASA
Great collection of maps via Data Center. I think I can chose locations in different regions via this bottom map and ask them to plot those elevations on a number line. I like that it gives an opportunity to plot negative decimals and fractions, absolute value, inequalities and opposites.
I am also thinking that topographical maps offer a nice opportunity for elevation change and rates. Since the number of lines between two locations represent a unit rate. For example if you have 1 location marked at 100 feet and another location is 5 lines away at 50 feet, this means that the unit rate represented by each line is (100 - 50)/5 = 10 feet.
I found this topological map generator here.
With New Orleans, I am thinking of showing it first on Google Maps, then showing an elevation or flood map to tell a different story. The original map of New Orleans doesn't reveal any story other than location (as it should), but the point is that different maps tell different stories. The data center also had maps showing poverty, population change, etc. They even have a series of power point slides. Furthermore, they have percents and percent change. Pretty cool!
Also, I just figured out that if you draw a path across a map and then right click it and select "show elevation profile" and adjust the altitude to sea level, you get a pretty graph of the elevation. Yay!