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GIS to quantify public access across the California Coast


Hi everyone! My name is Lucas Lowe, and I’m a student pursuing a degree in environmental studies at UC Santa Barbara (UCSB). This summer, I had the wonderful opportunity to work as an intern for the Channel Islands National Marine Sanctuary (CINMS) through the Bren Environmental Leaders Program here at UCSB. This summer, I had the opportunity to work in person at the CINMS building, where I collaborated with Dr. Jennifer Selgrath (project co-lead) and Kennedy Flavin (UCSB Bren ‘24)! 


My goal in this collaborative project was to use my knowledge of data analysis and geographic information systems (GIS) to quantify accessibility for California residents to their nearest Marine Protected Area (MPA), National Marine Sanctuary (NMS), ferries, and the public access points along the California coast. 


My first task was setting up the data: origin and destination points. The origin points for the network analyses were ZIP codes, block groups, and census tracts, all geographical units commonly used in demographic analysis. For these groups, I would use what is called population-weighted centroids, which is a center point representing the average location of residents within that specific shape area (see images below). 


A. ZIP codes of California       B. Census tracts of California      C. Block groups of California


To obtain the destination points for MPAs and NMSs, I would upload these areas as shapefiles and then upload the public access points. From here, I would create a 250-meter buffer around each public access point. If this buffer intersected an MPA or NMS, it would be isolated and considered for the network analyses. Our rationale for choosing 250 meters as our maximum distance from a public access point to an MPA or NMS is because 250 meters correlates roughly to a 3-minute walk. For people who are mobility impaired, this could prove to be more of a challenge, so anything outside of 250 meters was not considered.  I've copied an example below:



In this map, there are points within and outside of the 250-meter buffer around the nearby MPA (lime green). The large blue bubbles are the 250-meter buffers surrounding the points that are both within the nearby MPA (pink) and outside of it (dark blue). 


Interestingly, the public access point data was slightly outdated before this project, but thanks to the contributions from a team at California State University Channel Islands, we were able to use updated and more accurate public access points (thanks to assistance from Dr. Kiki Patsch and Dr. Dan Reineman)! 


After assembling the data, I began my network analysis. The tool I used was the “Closest Facilities” function in ArcGIS Pro. This function uses Waze real-time data to compute the network analysis. We ran all of our analyses on the set date June 25, 2022, at 11:00 AM. Although this date is specific, it was with reason:


  • June is a common month (with relatively good weather) when people go to the beach in California. The 25th was decided upon since Father’s Day takes place the weekend before, which could also provide inaccurate data. 

  • 2023 data was not yet available, and 2020-2021 was impacted by the pandemic. 2022 is the most recent year with updated data that isn’t as hindered by the pandemic. 

  • 11:00 AM was decided since that’s a time many attend or go to beaches. 


Hooray! The data is input. On to the network analysis! Copied below is a zoomed-in example of one of the “Closest Facilities” functions: 



The location of this map is Isla Vista, close to Santa Barbara, CA (the backyard of where I attend school). The pink circles are the public access points within 250 meters of the nearby MPA (lime green), the blue lines are the driving routes, and the green squares are the origin points (ZIP code population-weighted centroids). 


Once finished, the routes from each analysis (the blue lines from the map above) would be exported. Embedded in the routes files are the total time it takes for the drive (min), the distance (km), the origin point, the destination point, and the arrival time if departing at exactly 11:00 AM on June 25, 2022. These analyses are conducted 11 more times for ZIP codes, census tracts, and block groups going to MPAs, NMSs, ferries, and all access points respectively. 


Later this year, these routes files will be combined with equity and environmental justice (EEJ) indicators to see how the accessibility to public access points varies based on educational attainment, linguistic isolation, age, and a variety of other indicators.

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