The Willamette River, which flows north through downtown, serves as the natural boundary between east and west Portland. The denser and earlier-developed west side extends into the lap of the West Hills, while the flatter east side extends for roughly 180 blocks until it meets the suburb of Gresham. In 1891 the cities of Portland, Albina, and East Portland were consolidated, creating inconsistent patterns of street names and addresses. It was not unusual for a street name to be duplicated in disparate areas. The "Great Renumbering" on September 2, 1931 standardized street naming patterns and divided Portland into five "general districts." It also changed house numbers from 20 per block to 100 per block and adopted a single street name on a grid. For example, the 200 block north of Burnside is either NW Davis Street or NE Davis Street throughout the entire city.