Mapping and monitoring are two words that often go hand in hand, but it’s not always clear exactly where their differences lie. While the two processes are required for understanding various spatial relationships that exist on the planet, what each process looks like, why they’re done, and how they’re performed are quite distinct.
Defining Mapping and Monitoring
Mapping is the process of making a map for the purpose of creating a static representation of a specific location. The key benefits of creating a map are to help users navigate to their destination of interest, gain an understanding of relative distances from one point to another, and overall be aware of their general surroundings.
Monitoring is the process of analyzing changes that occur over time. This is done to understand the mechanisms of different relationships whether it be the results of a change made by humans to the environment, the results of changes caused by natural disasters, or any other cause and effect mechanism.
Mapping and monitoring are independent processes and don’t necessarily need to be done in unison, but when paired can be extremely beneficial for understanding how the surface of the Earth is changing over time.
Why Map? Why Monitor?
The reason for mapping is to create the most accurate depiction of a location as possible. This is especially important in GIS where every pixel must correlate to a specific coordinate. For this reason, it’s not just about accuracy in terms of the depiction of objects like building and roads in relation to each other, but that their positioned properly in terms of their exact location on Earth.
Mapped objects don’t change very often which allows maps to be reliable sources of truth for a number of years. You’ll see this in applications like Google Maps, Bing, and Mapbox where their base maps are practically identical every time you view them.
Maps create a foundation for monitoring the Earth’s surface. Without them, you wouldn’t know where or what you were looking at! The location that a map depicts acts as a control. Dynamic characteristics like population, weather, and other features change, but the location remains the same. This allows spatial analysts to incorporate a temporal element into their studies making monitoring a continual process and leaving mapping as a once-in-a-while process.
Mapping and monitoring are done to understand many phenomena and areas of study including:
- Land use (urbanization, deforestation, etc.)
- Politics (border conflicts, military, etc.)
- Food security (farmland, soil moisture, etc.)
- Pollution (air quality, public health, etc.)
- Ecology (species movement, algal blooms, etc.)
Collecting Data for Mapping and Monitoring From Satellites
The objective of mapping and monitoring are different and so are the data they use. While there are a variety of ways to map and monitor, when done together they often rely on two main data source: optical imagery and satellite imagery.
Optical Satellite Imagery
Optical imagery are images that are created using the visible light spectrum. They operate the same way your point-and-shoot or DSLR camera work but are utilized above the surface of the Earth instead of on it. It may also be referred to as aerial imagery.
The cameras and technology used to capture optical imagery allow for extremely high resolution images that are easy to interpret. Though they are taken above the surface of the Earth, they aren’t far enough away to capture the Earth’s curvature which may otherwise cause geometric issues when digitizing the data. This means it’s possible to be much more accurate when lining up pixels with a real world location.
Optical imagery allows for absolute accuracy making it possible for features to be traced and turned into simplified vector maps to represent a broad area. This imagery is a great data source for the purpose of mapping.
Challenges & Limitations
Though extremely useful and one of the most efficient ways to collect data, optical imagery does come with its limitations. Since images rely on the natural light spectrum, they rely on the sun to illuminate the Earth for clear photos, and that’s not always possible.
Even when the orbit lines up for your location of interest, clouds may still get in the way blocking any chance of capturing an image. Approximately 60-65% of the Earth is covered in cloud at any one moment.
This means the use of optical imagery isn’t reliable when you need to collect data on a regular cadence. It also is limited in the distance away from the Earth it can be utilized from simply due to cost. The technology needed for high-resolution imagery does not come compact or light. To send it further from the Earth to capture a larger area would requie much more jet fuel and rocket power than it’s worth.
Synthetic Aperture Radar (SAR) Satellite Imagery
An alternative to optical satellite image is synthetic aperture radar (SAR). SAR is and active sensor meaning that it is not reliant on the sun to illuminate the earth. As the satellites orbit the plant, the SAR will both transmit and receive electromagnetic waves towards the Earth to collect information about various characteristics. The data collected is run through various algorithms to create an image of the Earth’s surface.
Unlike with optical imagery technology, the physical characteristics of the technology needed to collect satellite imagery is much easier to send into space make it a much more cost effective option for collecting data regularly. Using radar makes it possible to collect data through cloud cover and without reliance on any kind external illumination.
SAR makes it possible to collect information about the Earth’s surface at regular intervals to analyze ongoing changes. This type of imaging system is extremely effective for monitoring purposes.
Challenges & Limitations
While the technology used to collect satellite imagery is remarkable, that doesn’t mean it’s easy to work with or understand. One of the main reasons this technology has not advanced as far or as quickly as others is because for a long time it was only used for military purposes and was illegal to operate otherwise.
Machine learning models help with automatically extracting key insights, however the data itself is not as interoperable as the data obtained from optical imaging especially since there aren’t standardized formats.
The Future of Mapping and Monitoring
The big question now is: What does this mean for the future?
Take it from Joe Morrison, VP of Commercial Product at Umbra, as he explains it on the MapScaping podcast episode The Problem With Satellite Data Is …That It Is Not A Commodity.
“Compared to optical there’sa really long road to go in synthetic aperture radiator and that means opportunity for the early adopters who can work on that really hard problem and crack that nut. But, it also means it’s going to be slower to see commercial adoption because people will get the data and be like, what is this?” he says.