See the Expansion Maps for orientation of the different areas.  The locations refer to their position in relation to the Original city.  Circle 1 represents those areas adjacent to the center and Circle 2 represents those areas adjacent to Circle 1 in expanding concentric rings around the original area given at the start of the game.  Given the pricing on the latter areas, these are actually in reserve and may be subject to change as the game expands.  Those expansions that have attached timed expansion quests upon unlocking are marked with TEC.