I think it depends on whether you're doing homebrew or premade. Premades generally have maps of any locations you need and in Pathfinder even without a premade adventure, or on TOP of the premade adventure there are info books on different cities you can use to provide info on locations, random encounters, local personalities, ect. But even with this premade stuff, they may have this whole city, but every house isn't marked out so you can throw in some original stuff of your own. If you're doing a homebrew, it depends on your story and how you're using the world. Sometimes the whole story will be based on a city so having a detailed city would be important because there would be quests in the sewers, the crypts, in someone's house, the castle. It would be important to know what area is what kind of location in the city, slums, market, noble quarter. But this is only if you're running a city-based campaign. Or even with a town-based campaign where everything's based out of one location to nearby ruins or other things but always returning to one town... If your homebrew instead is supposed to have a vast world, different countries and politics, the location centric approach is best with descriptions of anyplace where there won't be any events of import. If it's a journey to a central location, having a generic overview of the sections of the city and what can be expected there (eg Slums: poor people, taverns, pawn shops, tiny apartments, narrow streets; Market: Wide square filled with stalls one day a week, mid-class inns and taverns, eateries, craftsman shops/home combos.) You don't need every street, but a general overview of what is there, what can be found there and then additional notes of specific things players ask for that you put there. With a homebrew, it might just be best to keep it general and then build and elaborate WITH your players after making a general overview to start.