Sand, I know I hate it when no-one comments on my ideas, so here goes my not-politically-correct assessment: You can't show it because No one knows.

The predicted rise in sea-level may not even occur, as more warming might result in more snow, and no coastline change. The centrifugal forces of the spinning of the earth and coriolis forces mean it by no-means would be an even deepening for the whole earth.

Finally, we all know that the P-38 "Glacier girl" was buried under 268 feet of ice that formed since 1942, so I'm not so sure it's predictable where ice will disappear and where it will get deeper, warming or not.

And Miami is still one of the fastest growing cities in the world, with many 'green' celebs moving to those coasts. Mr. Gore's movie showed it underwater at the very start of the sea-level rise. Possibly these people really don't believe ?

I appreciate your comment but this recent report http://www.iht.com/articles/2008/03/12/america/coast.phpseems to represent real concerns about global warming and the resulting melt of ice. Nobody can seriously dispute the global warming anymore. Any topological map would indicate ground levels above sea level and a slight modification would indicate the changing coastline fairly easily.

What a boon for real estate speculators. They would know where to buy the property that becomes the next waterfront location. The tax assessors would also know where to boost the property valuations. Can't wait...

You say that this is to inform people considering purchasing this land of the potential for flooding in the near future, but if people are aware enough to check this check this resource, they should be willing to check a topographical map of the area, as such maps are available for most all of the planet, and usually free from the local government, at least here in the US. It is true that compiling this info for all to see online may make it more convenient, but perhaps it would be more suitable to suggest it as a realtor's database, rather than a google-earth feature.

Good idea. Important.

A whole earth topographical map would be invaluable for a number of reasons. Besides indicating what areas might flood given an even small rise in sea level, the map could also be used by forcasters and emergency personnel for both warning inhabitants and pre-positioning emergency equipment in the event of heavy storms (which we seem to be getting a lot more of recently). Also, it could be used for simulations by engineers building anything from roads to dams to predict ecological effects of their work. While topographical maps are out there in bits and pieces it would be useful to have a central site with all the information being updated constantly. In the US this task might be jointly undertaken by the geological survey service, national geographic society and, as you suggested Google as the platform for distribution of information. Even if the dire predictions happen later or not at all the data would still be valuable.

Take all of the boats out of the sea.

Yeah, think about it ;)

Nobody has a crystal ball into the future, but it is clear the planet is warming up and the ice is melting. I think this is a very good idea in raising awareness of what would happen if sea levels raised. Part of the prediction is storms will become bigger and less predictable, so even if sea levels rise one foot, it doesn't mean those three feet above sea level will escape from flooding. I doubt this idea would have much effect on property prices until we see some catastrophic effects of global warming. Flooding of homes is only one problem of many. Crop failure, food shortages, mass starvation, disease, financial collapse, and world war would likely happen before the rich nations suffer the worst consequences.