Coordinate Systems and Web Maps

Coordinate reference systems are ways to store and display a specific location on the Earth’s surface. Coordinate reference systems do three things:

1. They capture the location of a point

2. They have a unit of measure and

3. They use a mathematical model to describe the shape of the Earth

The Earth is often described as being a sphere, but that is only an approximation. The Earth is actually an ellipsoid, or a squashed sphere.  

Herein lies the challenge: taking data represented on an ellipsoid and flattening it. The way we communicate with each other is through flat surfaces. For example, it is common to use a printed map or a computer screen. If we want to communicate geospatial data, we will need a way to make the data flat. To further understand the challenge, think about peeling an orange. Let’s say you peel an orange and then try to take the peel and lay it out flat; it’s not going to be a perfect square.

This is where the separation of geographic and projected coordinate systems comes into play.

Geographic vs Projected Coordinate Systems

• Geographic Coordinate Reference System (CRS): Represents locations on the Earth’s curved surface using angular coordinates (latitude and longitude). These systems are ideal for storing geospatial data because they provide a consistent, globally interoperable foundation. They are the standard for web mapping applications, GPS, and data sharing across different systems.

• Projected Coordinate Reference System (CRS): Takes geographic data and converts it onto a flat (planar) grid for use within a specific area. Common examples include State Plane, UTM, and Web Mercator. Projected systems excel at surveying, engineering, and high-accuracy local measurements (where distortion needs to be minimized inside a defined zone). They are typically used for display, cartographic products, or analysis that benefits from linear units and planar calculations.

Geographic CRSs, such as EPSG:4326 – WGS 84, are the recommended storage format for our platform because they ensure broad compatibility and straightforward transformation. Projected CRSs are recommended for display and any workflows that require high local positional accuracy, such as engineering drawings or precise asset measurements. Data can be transformed between the two as needed.

Mercator and Web Mapping

Many web maps use a Mercator-style projection to take 3D geographic coordinates, latitude and longitude, and convert them onto a 2D flat plane. The most common version used today is Web Mercator (EPSG:3857). It is the industry standard for web mapping because it:

• Preserves local angles so that shapes remain recognizable

• Creates consistent square tiles that render quickly across zoom levels

Storage Best Practice: Web Mercator introduces severe scale and area distortion away from the equator. Because of this distortion, never use Web Mercator (EPSG:3857) as your authoritative data storage format.

• For web-first workflows: Store raw data in a geographic CRS like WGS 84 (EPSG: 4326)

• For engineering/local government workflows: Store data in your local projected system, such as State Plane or UTM, and only transform it to Web Mercator when publishing to a web viewer

Coordinate Reference Systems Identification

You may notice coordinate reference systems labeled with codes such as EPSG:4326 or EPSG:3857. An EPSG code is a standardized identifier used around the world to refer to the same coordinate reference system. There are over 10,000 codes maintained by the Geomatics Committee of the International Association of Oil and Gas Producers (IOGP). These identifiers make it possible for GIS software around the world to reference the same mathematical definition without ambiguity.

There are thousands of EPSG codes, each representing a specific geographic or projected coordinate system. Some of the most common include:

Putting it all together

CivicPlus Asset Management follows the industry standard of storing all spatial data in EPSG:4326 (WGS 84) because it provides the best foundation for managing geographic information. With this, we get several advantages:

• Preserves accurate geographic locations.

• Supports reliable measurements and spatial analysis.

• Simplifies data sharing and interoperability.

• Uses the same coordinate system as GPS and many GIS applications.

• Provides a consistent standard across all geographic regions.

Because the data remains in its original geographic coordinate system, it can easily be transformed into other coordinate systems whenever needed.

Secondly, to project our GIS data, we use EPSG:3857 or the pseudo web-Mercator projection. This is an industry standard as well because it:

• Preserves local shapes such as roads, buildings, and other assets, and direction

• Optimized for fast map rendering because tile size and shape are standardized across zoom levels

• Easy to align data on top of basemaps

• Familiar visual appearance such as those used by Esri, Google, or Bing

Conclusion

To provide consistent, accurate, and high-performing maps, all GIS data in our platform is stored using EPSG:4326 WGS 84 and displayed using Pseudo Web-Mercator EPSG:3857.  This is the industry standard used by modern web mapping platforms. This approach allows us to keep location data accurate for analysis while ensuring maps load quickly and are easy to view and interact with online.

Additional Resources

• Geographic vs Projected Coordinate Systems by Esri