I didn't think much about this wisdom until last night while working out ideas for my invasion novel. Not every story needs a map. If you're doing a story along the lines of My Dinner with Andre, all you need to know is that there are two guys (dudes, if you will) talking over dinner. Can you see me writing My Dinner with Andre? Yeah, I can't either.
But here's what I did do. I looked up a set of maps from 1898 when my invasion story is set. I wanted to know how expansive the major countries of the world at the time were. It's a reasonable thing to do. If you write a present-day story set in Broken Bow, Oklahoma, you'd look up a map of it on Google or Mapquest so you get an idea of how big the town is and where the roads are, the houses versus the stores or the school.
I didn't find a world map for 1898, but I did find a map of the continents from North America to Australia. Once I saw where all the countries were, I moved on to what characters I wanted to write about. This partitioning of the globe had an unexpected benefit. With with one, I asked myself, "Who in this place would be interesting to write about?" They don't have to interact with each other. They only need to be interesting.
The African map stands out as a good example of character possibility for me because I came up with what I think are two really interesting ones. The first character is a South African guerrilla fighter. The idea popped into my head because at this time Britain and South Africa were just about to get into the Second Boer War, which helped give rise to the word commando. Commandos fighting aliens? Sounds cool to me.
The second character is Winston Churchill. You can laugh at that. It's healthy. The idea of Churchill - old, fat, and chomping on a cigar - fighting aliens is as absurd as Lincoln fighting vampires. But in 1898, Churchill was a 24-year-old cavalry officer in Sudan. I don't have to change Churchill himself to get started, only his circumstances. I'm biased, of course, but I have every right to be. I'm the writer.
Now I'm not saying that looking at a map solved my story problems completely. I did have to dig a bit into history. As far as how the invasion will unfold, I'll have to go back, see where everyone is, and move them around like chess pieces. But the maps did give me a good starting point and spared me from a lot of confusion. The same might work for you.