The LA River is a complex system with many layers of information and data. To better understand conditions along the river, the LA River Master Plan used over 200 ”river rulers” to organize and collect existing data and new data that was created as part of the Master Plan process.

The river ruler is a vertical straight-line diagram that represents and takes measure of the entire 51 miles of the LA River.

The vertical axis (height) of the river ruler represents the 51 miles of the LA River, with river mile 51 at Canoga Park in the West San Fernando Valley at the top of the ruler and river mile zero at Long Beach where the LA River meets the Pacific Ocean at the bottom of the ruler.

The horizontal axis (width) of the river ruler varies depending on the data being shown. Unless otherwise noted most river rulers show conditions found directly at the river channel. Where a centerline is shown, conditions found immediately along the left and right banks are shown. Many river rulers show conditions within the larger river corridor up to one mile away from either side of the channel.

Lastly, some river rulers have variable widths to show the magnitude of a particular condition and have reference lines and the unit labeled. Examples of a variety of ruler types can be seen at right.

The benefit of the river rulers is that multiple rulers can be aligned on a single page so that multiple categories of data can be assessed easily side by side. Comparing across multiple categories at multiple locations along the river in a single drawing is essential for understanding the river as a complex urban and ecological system and for recognizing where planning and design proposals can achieve multiple benefits at a particular location.

Throughout the LA River Master Plan, river rulers are typically used in tandem with maps that show the same data in the context of the broader LA River watershed. In the inventory and analysis sections, the rulers are commonly used so that various datasets can be compared.