Carmen Leedham

Senior GIS Analyst

Photo of Carmen Leedham

Education: B.A. in Geography (San Diego State University)

The following profile was compiled by Jessica Embury (San Diego State University) for the Encoding Geography initiative. To learn more, visit:

Please describe your job, employer, and the primary tasks you perform in your position. 

I work for the County of San Diego, Health and Human Services Agency in the Office of Business Intelligence. The office I work for is a support department that works with other offices within the Health and Human Services Agency, such as Aging and Independent Services and Public Health Services. The primary tasks I perform revolve around GIS. I create static maps, web maps, and perform geospatial analysis to answer questions posed by leadership and my coworkers. For example, I performed geospatial analysis to convert tabular data into spatial data to answer, “How many CalFresh recipients live in each district in the County of San Diego?”  

What is your educational background? How did you initially discover geocomputation and why did you ultimately choose a career that uses geography and computer science? 

The people I met during my education have been instrumental in the trajectory of my career and have been very important to me. I first came into contact with geocomputation after completing a cultural geography course at Grossmont College with Professor Mark Goodman. He told me what a career in geography might look like and he encouraged me to enroll in an “Intro to GIS” course. At first, I did not understand anything, but the professors were so helpful and they made time for their students. I never had any computer classes in high school or middle school so learning how to work with a computer was very new to me. 

About a year later, I applied for an internship with the County of San Diego, Health and Human Services Agency in GIS. From there, I started to learn important skills, like how to work in a professional office, how to email people, and how to communicate with people in a professional setting. I started to really like it and see a life for myself working in GIS for a local government.   

At the time, I was 18 or 19 and I was going through a lot – I had unstable housing and food insecurity. I wasn’t sure how I was going to make it day-to-day or month-to-month. I saw GIS as a path to achieve the things I wanted: stable housing and a little bit of fun money. From that point forward, I started thinking about how to get a career in GIS as quickly as possible. In May 2019, I completed the GIS technician certificate of achievement at Mesa College – the requirement to get an entry level job in GIS with the County of San Diego. In September 2019, I got a full-time job with the County of San Diego in the Land Use and Environment Group. Since then, I’ve been with the County of San Diego, moving up and honing my skills in GIS.  

When thinking about geography, what specific background knowledge and conceptual ideas are important and useful to know? 

I feel like geography – both physical and cultural geography – cannot be separated from GIS or geocomputation. The foundation of geospatial analysis builds upon cultural and human relation to place and space throughout time. Likewise, GIS builds upon physical geography and knowledge of our surroundings.  

I mainly focus on cultural geography and the socioeconomic conditions of people within the Health and Human Services Agency of the County of San Diego. So, with geocomputation, we run the risk of turning people, plants, and places into numbers or into commodities and binaries. Through geography, we can return people from numbers and binaries back into real life things that have special life circumstances and value to one another.  

Conceptually, an understanding of sustainability should be gathered prior to working in geocomputation. Our actions have consequences, both positive and adverse, and this is something we should take into consideration in our day-to-day interactions. Our work always revolves around the three pillars of sustainability: people, profit, and planet.  

When thinking about computer science, what specific background knowledge and conceptual ideas do you think are important and useful to know? 

I recommend starting with the basics like: What are hard drives? What are the different types of hard drives and what do they do? What is the central processing unit of a computer? What’s a good one or a bad one? How much memory does the computer or device have?   

Then, you need to understand different types of software. Think about your needs and what software can meet the questions posed by your research. From there, you have to learn how to use the software. What file type does the software use? How are these files opened in the software? How are they saved on your computer?   

When I started GIS, I went to buy a laptop and I thought, “Okay, I need something that can handle the amount of data I’m going to be running and the strain I’m going to be putting on my computer.” I had to look at things like core memory and plan accordingly, because there are times that your computer will be overworked.  

What procedural knowledge is important to know, from either geography or computer science, in your work? 

It is important to know how to isolate your question, so things like the scientific method can be helpful. You don’t need to follow it exactly, but it can help you identify methodology to solve the question. What information do I need to solve this problem? Does this information exist in the format I need and, if not, can I create this information or do I know someone that can assist me in gathering this information? 

From there, test your methodology. Be flexible because a lot of things aren’t going to work and you need a plan B, C, D, and so on. It’s very helpful to know people within your line of work so you can ask questions and be nudged along in the direction you need.  

Can you share a specific example of how you apply geography and computer science to analyze and solve problems related to important issues?  

Since March 2020, when the novel coronavirus entered the United States, the County of San Diego tried to get ahead of it. We had public health scares in the past, like the Hepatitis A outbreak, so we had a little bit of a framework. 

My office develops and maintains a publicly available web map application for locations with publicly funded hand washing stations and public restrooms targeted for use by individuals experiencing homelessness. The County of San Diego hoped to prevent the spread of COVID-19 by placing hand washing stations and portable restrooms in locations that have known homeless encampment sites.  

What kind of geographic questions did you ask and think about during this project?  

The Office of Business Intelligence did not have to decide where the washing stations would go, but we relied on spatial data about homeless encampments to show hotspots and clusters of people experiencing homelessness.  

Someone else using this data would say, “Let’s place a hand washing station on this street where there are a lot of people experiencing homelessness,” and from there, I would receive the name of the street that this hand washing station is on and other internal information, such as how long it will be serviced or problems with the station itself. I would then convert this tabular data into spatial data. Addresses are not spatial data because there are no latitude or longitude coordinates connected to them. These coordinates are necessary to perform geocomputation, otherwise, it’s just data on your computer.  

We ended up creating a public web map application. I published the data as a hosted feature service on ArcGIS Online and I update it every so often. I had to think about possible problems with sharing this data with a large audience. We didn’t know how many people from the public would be looking at this map and a lot of pings could cause the map to be slow or stop working. I had to think of these problems ahead of time because if this map were to go down then the public would ask questions.   

In doing this project, I had to understand the software I was working with and the data formats. I had to think about whether the public would have problems viewing the map, and whether the data was understandable and digestible to the audience.  

What types of data did you acquire to support your project? Please identify up to three data sets that you utilize the most. 

I frequently perform geocoding to assign latitude and longitude to an address using an address locator. An address locator consists of different road networks of polylines within an area. For example, SANDAG publishes a dataset called “roads_all” that contains road types, road names, and address ranges. The address locator matches the tabular address data to spatial data in the road network and then converts the tabular data into spatial data. 

Since we have so many geocoding requests, we work on building the best address locator to match with the most addresses in the least amount of time and with the highest accuracy. We use “roads_all” from SANDAG as well as a road network from ESRI. We also use TIGER/Line shapefiles from the US Census Bureau because sometimes people have mailing addresses outside of the County of San Diego. I combined these road network datasets to produce a composite address locator that I worked with daily for this project. I also used the point in time homeless count from the San Diego Regional Task Force on Homelessness as well as internal data sent by my coworkers in neighboring offices. 

What types of content, knowledge, and skills did you use to evaluate the project and analyze the data gathered for your project? 

Something I wasn’t prepared for was the amount of general skills, like Excel and Word, needed to perform day-to-day tasks. Communication is another huge part of my job, so I have to understand the needs of the project, the questions answered by the project, and how to provide deliverables to the customer. The customer could be one of my coworkers in an office or it can be the public. 

With the hand washing stations and portable restrooms web map, I needed to make sure that the data was always up to date and that the data could handle being updated frequently. I needed a huge understanding of ArcGIS Online and that suite of products. Another aspect was working with firewalls. I work in a secure network that the public cannot access, so I needed to get private data to the public and ensure that it met requirements to share with the public.   

More specific skills I used are geocoding, creating an address locator, creating web maps, and creating web applications. 

How did you apply geography and computer science to communicate the results of your project? Do you have a recent product or publication that you could share with us as an example? 

The web map of hand washing stations and portable restrooms is on 211 San Diego and contains hand washing station icons and portable restroom icons. Using this map, you can enter an address to see where the nearest hand washing station or portable restroom is. You can click on an icon and get additional pop-up information.   

To create this map, I had to use Excel, bring the Excel spreadsheet into ArcGIS Pro, geocode the data set with my composite address locator, create a feature class in my geodatabase, and publish it online for the public to view. Once published on ArcGIS Online, the data is stored in the cloud and is referred to as a hosted feature service. I had to ensure the sharing capabilities were correct so other people – like students – can bring this data into their own maps. Then, I had to make sure that there were no technical problems on the backend which would make the map stop working.  

When reflecting on your work, how does it align with your personal values and your community/civic interests? 

I used to be a customer of the County of San Diego and I used to receive CalFresh. I saw how the County of San Diego helped me, I see how it helps other people who are in that situation, and I know that some good is being done. That is rewarding to me. The things that I care about are making sure that people are able to live well and thrive, rather than just survive and get by. It’s nice to know that there is a group of people working to make sure that the basic needs of our community are met, and that resources are available. 

For me, public web maps are key because we can show the public that there are resources available. People don’t always know what’s available to them and we need to share the work that we’re doing and what the County of San Diego provides. I like working for an organization that is helping people and making sure that things are working as they should be. It makes me feel good — like harm reduction is occurring.   

This material is based upon work supported by the National Science Foundation under Grants No. 2031418, 2031407, and 2031380 (Collaborative Research: Encoding Geography – Scaling up an RPP to achieve inclusive geocomputational education). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation