NB: Java applets no longer work at all in the Chrome browser, as support for such plugins was discontinued by Google.
Having done an interactive topographic Map of Mars, I just couldn't stop: I had to do one for Venus as well.
Alas, Venus is both more difficult and less interesting. More difficult because accurate data is hard to come by. NASA's Magellan mission has used radar to create a topographic map of most of the planet's surface, but this information is considerably less accurate than the Mars Observer Laser Altimeter data. There are also areas not covered by Magellan radar.
Even so, I was eventually able to locate a suitable data set and modify the Java applet below to demonstrate what Venus would look like, were it flooded with an ocean. As it turns out, Venus, once dubbed Earth's "sister planet", is a lot less Earth-like in this respect than Mars! Whereas Mars has a well-defined "coastline" and an ocean (although the true nature of this northern depression remains a subject of debate), the surface of Venus lacks such coastlines and easily identifiable continental landmasses. Venus is also a lot more flat than Mars; set the altitude to -1200 meters, for instance, and you'll notice that all oceans will have completely disappeared. (In contrast, the deepest spot in Earth's oceans is more than 11,000 meters under mean sea level, in the Mariana trench.)
A Venus topographic map is also much less practical than a Martian one. Whereas the problem on Mars is cold and vacuum (both of which can presumably be dealt with by a future, multi-generation terraforming effort), on the surface of Venus the temperature is hot enough to melt lead, and the atmosphere, at 93 times terrestrial pressure, contains some of the most corrosive gases known to man.
To use this program, set the sea level altitude to the level of your choosing (meaningful values are between -5000 and 10000 meters), and click the Redraw button. On slower computers, it may take a bit of time for the map to update itself. Gray represents areas not covered by Magellan radar.
This program utilizes data downloaded from NASA Planetary Data System node at Washington University in St. Louis. The inspiration came from the Astronomy Picture of the Day Web site.
To see information on "live" planetary probes (alas, none near Venus at the moment), please visit my Deep Space Probes page.
