Visualizing California's Protected Areas

Updated: Mar 31, 2021

A study of Esri's various methods of data visualization.


The state of California covers over 424,000sqkm. Its 58 counties range in size from 113 - 50,000sqkm. As of January 2021, there are over 14,000 protected areas on file, administered by government agencies and non-profit organizations.

California Map - ArcGIS Map Service

These include California State Parks which make up 270 units alone. Protected areas may even be privately owned. For being the most populous state in the country, 49% of its land is protected. You may even spy the occasional Zebra grazing along Highway 1 near the town of San Simeon, a relic of the Hearst Castle Zoo built in the 1920s and remains protected to this day. (Source: Wikipedia,

Here, I explore three Esri platforms for data visualization and interpretation of California's protected areas. The first is using ArcGIS 10.7, leveraging its powerful and diverse map layout tools. Then, I publish the map to ArcGIS Online to make an interactive web map. Lastly, I create a web mapping application as an informative end-user tool.

ArcGIS 10.7 - Data Management

The data for this study was downloaded in shapefile format from the CPAD (, imported to a file geodatabase and projected to the study's California Teale Albers coordinate system. Click on the following to access original data sources: Protected Areas, Counties

The protected areas database contains over 78,000 holdings each populated with various attributes the county it resides in. While the holdings mapping unit has a lot of useful information, it is less useful for visualization on the state scale.

By performing a dissolve function by county, we now have a summarized table for total protected area by county - just 58 records and better suited for visualization purposes. The variable I want to map is beginning to take shape; the percentage of total county area that is protected. Now I can add a new field and calculate the total area with protected status for each county. Let's take a quick peak at the resulting map.

Why is the county layer extending past the protected areas so consistently along the California coast? Are no coast lines protected? Upon further inspection into the metadata provided for the Counties shapefile, it turns out that oftentimes coastal county boundaries will include a 3-4.5 mile 'outer limit of jurisdiction' ( Be wary of this when performing area analyses on shapefiles as this will inflate your totals. To remedy this, I used the clip tool to clip the counties layer to a land-based state boundary layer provided to me in Esri's Mastering ArcGIS data bundle.

One I added a new field to calculate county areas in square kilometers, I joined the layers together using the Join tool, with the County field used to base the join on. Finally, I added one last field and used the field calculator to input:


Now we're ready to visualize!

ArcGIS 10.7 - Thematic Map

ArcMap (ArcGIS 10.7) has many powerful visualization tools that we'll explore here. First, I'll verify some classification elements. From the workflow detailed above, each county contains the percentage of protected area, ranging from 1.1% to 94%. Sturge's formula indicates the ideal number of classes for this dataset is 7 and, because the data is in ratio form, the most appropriate classification method would be

Equal Interval. Not only are percent intervals easily understood by the reader, but the number of classes is also ideal for portraying information in a thematic map. A simple dual-color ramp provides enough differentiation between each class.

Next, a word on base maps. Base maps are incredibly useful for visualization, giving the reader perspective and information otherwise omitted in thematic mapping. But they can also distract the reader and cause clutter. Be sure to consider their contribution to the maps you make. For this study, I wanted to feature California's coastline as it relates to protected areas without overly saturating my map with lots of colors and structure. As an ideal compromise, I followed an expertly written article on a feathering technique using multiple ring buffers in Esri's Newsroom Publications, ArcWatch. The resulting map is below:

Notice how toward the northeast and southwest the base map fades out. This is such a neat workflow with endless uses! Secondly, the county labels are formatted by class, allowing light labels to overlay dark polygons and vice versa for light polygons.

The shape of the features in the map being displayed will dictate the amount of free space for other map elements. Luckily, in this study, the shape of California offers ample free space for critical map elements and other infographics. I'll take this opportunity to work with the graphing capabilities in ArcMap, add an informative blurb for context, and finish with critical map elements including scale and data sources.

And there we have it. An elegant, informative thematic map featuring the distribution of protected areas by county for the year 2021.

ArcGIS Online Web Map

While the map I made in ArcMap is visually appealing and informative, I am restricted to sharing via pdf or image file. That's where ArcGIS Online's sharing power comes in. ArcGIS Online (AGOL) enables you to share your maps in an interactive way, enriched with dynamic layers and customized pop up dialogue. The reader can zoom in and around the map and add more from AGOL's collection of open layers. As my first experience with the platform, the California map served as an ideal map to explore its functionality.

Once the layers were published to my content via ArcMap, I toured legend formatting and base maps. I customized the pop up window to include a chart of the selected feature's attributes. By using the HTML source, I could write the chart parameters and formats inside the text window which adds a nice touch to the map.

The web map can be shared publicly, to your organization, and to specific groups you participate in. The overview tab provides plenty of space to describe your map's purpose and utility to readers - be sure to fill it in before sharing!

ArcGIS Online Web Mapping Application

The web map is a great addition to our bank of visualization methods... but there's more! Now that I have a web map set up, I can create a web mapping application to enhance the reader's experience with various dynamic widgets and infographics. In addition to increased visualization, Web Apps can be shared to anyone via URLs. Check it out right here!

Using the web app, I created a contextual guided tour of California's protected areas for any reader to learn from and enjoy. The three Esri platforms explored here provide modern, professional and very user-friendly ways to share information. And the buck doesn't stop here - next I want to explore Esri's Story maps and ArcGIS Experience Builder. Stay tuned!


Emily Gillis

GIS Specialist in the making

© 2021 Emily Gillis

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