Looking at it more closely, I think the real numbers may be between what I did before and a 60 meter contour from the “new” USGS map. The newer USGS map seems to be closer to real altitudes than the older one was.

I am now considering making an entirely new map that sets the ocean at 60 meters, and then shades the zone between 60 and 114. That would represent where the sea would be if most of the glacial ice melt, allowing room for transgression and isostatic effects. So, everywhere below the 60 meter limit would be definitely under water and everything above in the shaded area would vary with local conditions.

The scales on those two maps are not the same. I used the map you see in the post, and it is unaltered. The way I did it is correct for about 80 meters if the map is correct. I’m not sure how to reconsile the scale difference, or what the source of that is. I’ve been considering redoing this at some point, maybe sooner than later! But I do not assume the original is wrong simply because there is a difference. Note that in your look comlaring with the other map, some seemed off and some seemed OK. ( If I recall correctly, originally there was no scale and i asked for one to be on… )

By the way, after i did mine, another was done by NGS and they are very similar.

OK, I’ve looked more closely at your original post from June 18, 2013. You linked to the full-sized USGS map… http://pubs.usgs.gov/of/2005/1413/fulltopo.htm

They must have taken a map that used feet and converted it to meters, otherwise the strange choices of elevations make no sense. 8 meters = 25 feet, 54 meters = 175 feet, 114 m = 375 ft, etc

For that map I see 5 gradations of blue from 0 meters to 114 meters on the map key:

0 – 8 m = 0 – 25 feet =dark blue
8 – 54 m = 25 – 175 feet = 2 shades of lighter blue
54 – 114 = 175 – 375 feet = 2 shades of very light blue

If we assume the unlabeled subdivisions are midway between the labeled points, then we get this:

0 – 8 m = Darkest blue = 0 – 25 ft
8 – 31 m = 2nd blue = 25 – 100 ft
31 – 54 m = 3rd blue = 100 – 175 ft
54 – 84 m = 4th blue = 175 – 275 ft
84 – 114 m = 5th blue = 275 – 375 ft

So you can make the argument that the 4th blue color should be submerged, even though it is a bit above the 80 meters of total ice to melt. If you add in thermosteric expansion, we should be able to get to 84 meters.

Looking again at your final map showing future submergence, it looks like you have taken away all blue colors, including the 6th blue from 114 -137 m, and possibly the blue-green color up to 160 meters.

That’s how you get an ocean bay in central Illinois.

Look again on the original USGS map at the coastal plain of Texas and Louisiana. It is easiest to see there – each color subdivision is wide enough to distinguish.

I hate to be so critical, but I think an accurate map of this potential inundation is vital to help communicate the risks. And the Karma aspect of pointing out how BAU will flood out so many deniers in the Red southern states is too good to pass up.

Thanks again for you efforts.

Info sources:
I just used the free USGS topo maps here: http://www.mytopo.com/maps/

Fort Smith AR is the first place I looked, it is on the OK border, elevation 400 feet, GPS Coordinate: 35.3870907, -94.440622

Again, this is an excellent map. I would love to use it whenever a denialist argues that there’s no major danger from BAU warming. There are a lot of denialists here in the southern US. If they see their local area is slated for submergence, it will hit home.

But this message is ruined if they can immediately see obvious errors.

wehappyfew: This is based on topographic data supplied by the USGS. That does not mean it is totally accurate, but I’m not sure why national data supplied by the USGS would be wrong. I don’t think there is an issue of color interpretation by me, because that was just taking the pixels supplied by USGS and deleting all the colors below a certain altitude. There could be a number of reasons why there is a difference between what you are saying and this map, but to begin to think about that you would need to supply information on your sources. Thanks for the comment.

You have the Gulf of Mexico encroaching into Oklahoma along the Red and Arkansas Rivers. But the Red River is at 300 feet elevation at the Oklahoma border, and the Arkansas River is at 400 feet as it leaves OK. I think there are similar problems all along the proposed new seashore. Maybe a problem with the way the colors were interpreted by your map software where ever the slope is gradual. In steeper areas, its fine.

So the Hudson and Ticonderoga Seaway is valid. That will be a very interesting change to the local geography.