Map Details

This mapping application allows a user to interactively trace and indentify storm water features by water flow direction along the storm drain systems within Los Angeles County.

Usage Directions

Tracing can be conducted upstream, against the flow direction, or downstream, with the flow direction. Begin by zooming and panning to the area of interest, then click the "Select Start Location" button and use the cursor to select a point feature asset (maintenance hole, inlet or outlet) or pipe intersection point to set the trace point of origin. Selecting a location midway along a pipe may not provide desired results and only one start location can be provided at a time. Note that the point must be placed within 500 feet of the desired start location, the analysis will automatically snap the point to the nearest storm system point asset within the tolerance. Next select Downstream or Upstream, if upstream is selected, parcels can be visually filtered as well. Note that this adds to the processing time.

Flow along lines can also be selectively blocked, excluding them from the analysis, by using the "Set Flow Block Locations" button then clicking on the desired pipe(s). Multiple flow block locations can be selected.

Next select "Run" to start the analysis, depending on the selected location and options this may take up to a minute. Afterwards the display will update to show the results on the map and within the results window. From here the results can be explored and/or exported as a CSV table or a .zip containing the GeoJSON files.

The selection and/or results can be cleared at any time by selecting the "Clear" button.

Disclaimer
This is an unofficial personal project, I have no affiliation with any Los Angeles County public agencies, and I receive no compensation for this application. All provided data and results should be used for reference or demonstration purposes only. The data used in this analysis tool are modified from the source with data being split, merged, and added as needed, to meet the project's requirements and are not necessarily reflective of the original source data. The source data was acquired from the LA County Department of Public Works Storm Drain portal website and are also available from the County's ESRI MapServer. I hold no responsibility for the accuracy of these data or any decisions made based on information provided here.

Contact Me
If you have any questions, feature suggestions, comments, or notice any errors/bugs feel free to email me at

You can see my other projects under my projects section and you can see a description on how I made this map here.

You can visit the GitHub repo for the overall website project here and the repo for the website/Esri JS API application here.