It’s much more important to know your local geography when writing urban fantasy than it is when writing run-of-the-mill fantasy. You do need to be consistent in your geography when writing anything, but with regular fantasy, you can make the land up. In writing urban fantasy, it’s vitally important that you know the city that you’re using as a setting, because otherwise you’re going to get called out. This is doubly true if you decide to write about a city that you’re not intimately familiar with. If you must write in detail about a place that you’ve never been, be sure to get as many pictures and maps as you can, but if you can avoid the problem altogether, do so; your readers will thank you.
In this day and age, getting the lay of the land is easier than it used to be. If you’re reading these words, you have easy access to satellite images of the whole world. There’s a lot that you can discover about your city, even if you’re a lifelong native, by seeing it from a different angle that you can’t get just by taking a walk. This was impressed on me recently when I was flying back to Philly, a city which I’ve lived in since birth. Out of the window of the little prop plane I was in, I could see the city stretched out beneath me. On the plane’s final approach, I spotted a group of houses that looked as if they had been abandoned for at least the past decade, which immediately got my mind ticking, wondering who lived there, what they did, and why they moved out.
Getting the lay of the land also means taking to the streets, though. There’s a lot that can be discovered by taking a good long walk, and maybe even getting a bit lost. When you’re all turned around, especially in a city you know well, you often find things you might never have seen otherwise, and that can help you as a writer. It’s by taking chances that you discover the obscure, and therein may lie a thousand stories. This doesn’t mean being unsafe, though. A back alley is something totally different at night than it is in the daytime, but if you’ve seen one shady back alley at night, you’ve got enough to know what every other alley is likely to be like without putting yourself in danger.
So, my advice to you is to go out and see the place that you’re writing about, whether that means walking, biking, driving, or even flying. It might just be what you need to push your story to the next level, and it will almost certainly make your descriptions of setting feel more realistic to your readers.