When Pew released similar data in 2011, Slate and the New America Foundation created an interactive map showing how the population was distributed across the country. (The image below shows a still from that map.)
At that point, Nevada was also the front-runner, with a slightly lower 7.2 percent of the population estimated to be undocumented.
2. It has a fast-growing Hispanic population in general.
Even without considering the population that is undocumented, Nevada has one of the fastest-growing Hispanic populations in the country. Since 1940, the number of Hispanic residents in the United States has increased rapidly.
Compared to other states, Nevada's Hispanic population isn't that large. But when you consider the percentage of growth since 1980, Nevada stands out.
Hispanic population growth since 1980
Only North Carolina and Georgia have seen more rapid growth in their Hispanic populations than Nevada.
3. It's increasingly Democratic.
There's another reason that Obama likely chose Nevada: It's swung toward Democrats in recent presidential elections. The chart below shows how much more Democratic (above the zero line) or Republican (below) Nevada has voted in presidential races over the last 100 years compared to the country on the whole. Since 1980, it has gotten more and more Democratic relative to the whole country -- while its Hispanic population has grown quickly.
The change in Georgia and North Carolina, incidentally, is not as dramatic. Georgia's tilt to the right has stalled; North Carolina has become more Democratic more slowly.
If you're going to do a presidential event aimed at undocumented immigrants with an eye toward long-term politics, it's hard to see why you'd pick anywhere besides the Silver State.