Technically, Seoul is made up of several cities that have merged together. There is no clearly-defined border for where one ends and the next one starts. However, because of the situation with North Korea – technically, the North and the South are still at war and have been for nearly sixty years – the city is run as a special administrative region, which means the structure of the local government is slightly different to the rest of the country. If you zoom out, you will see a purple line encircling the city (though it in no way resembles a circle); this marks the boundary of the Seoul adminstrative area. If you switch to map view on my entry, you can see if your yourself. Since there were no rules that specified any boundaries to work within in the city, I just assumed that anything within that purple line was fair game.