August 2015
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GIS Case Study – City Boundaries in Los Angeles County

Department of Public Works (DPW)

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Problem: Precisely locating city boundaries on the ground is crucial for infrastructure management and construction project planning. In Los Angeles County, it is standard practice is to show accurate city boundary locations, where applicable, on all survey maps being submitted for recordation. In order for land surveyors to legally locate these city boundaries on the ground, legal descriptions of territories incorporated and annexed by Los Angeles County’s 88 cities need to be routinely retrieved. Searching through thousands of documents, many of which over a century old, to locate the exact description, has never been an easy task.
Solution: This application provides a powerful yet simple, quick, and user-friendly method to look up city boundaries and retrieve related documents such as incorporation, annexation, and detachments maps and legal descriptions, by location. In addition, the city boundary GIS data used by this application is available for public downloading at the Los Angeles County GIS Data Portal.

For decades, city boundaries, annexations, and detachments were meticulously updated by hand on several dozens of large linen wall sheets. When someone needed a legally described portion of any city boundary, too much time and effort were needed to search these wall sheets for the instrument name/number and locate the correct document.

As part of the Los Angeles County Digital Cadastral Landbase development using CAD software in the mid-1990s and later on geospatial technology, these wall sheet maps were digitized and over the years thousands of city boundary documents were scanned and uploaded into the Document Management System. This process produced GIS files for the city boundaries, annexations, and detachments. Finally, all these files for the 88 cities were merged into a seamless countywide GIS layer and moved to a public-facing web server along with the scanned documents.

Feel free to visit the City Boundaries and Annexations/Detachments webpage on the Los Angeles County GIS Data Portal. In addition to downloadable GIS data and an online viewer, a mobile-friendly version of this GIS viewer is available using ArcGIS Online. Large size annexation maps for the 88 cities and in PDF format are also on this webpage. Furthermore, a link to the Land Records Information website, hosted by the Los Angeles County Department of Public Works, where thousands of scanned recorded surveys are available free of charge, is provided on the webpage.

Contact:  Thierno Diallo, PE ( – (626) 458-6920



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