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What Is an EPSG Code and Why Does It Matter in GIS?

  • Writer: Anvita Shrivastava
    Anvita Shrivastava
  • 14 hours ago
  • 5 min read

Geographic Information Systems require precise location information. Each point, line, polygon, satellite image, orthomosaic from drones, digital elevation model, and spatial database must have an exact way of describing where it lies on Earth. That is when EPSG code plays its part.


The EPSG codes are popularly used in GIS, remote sensing, surveying, web mapping, photogrammetry, and geospatial applications to determine the coordinate reference systems (CRSs). It will be useful to know the principles of EPSG codes to avoid possible mistakes like displacement of layers, mispositioned maps, measurement errors, etc.


EPSG Code
EPSG Code

What Is an EPSG Code?


An EPSG code refers to a unique number used in defining a coordinate reference system (CRS) or other types of geodetic reference systems.


Examples include:


  • EPSG:4326 - Geographic coordinate system WGS 84

  • EPSG:3857 - Web Mercator projection

  • EPSG:32633 - WGS 84 / UTM Zone 33N

  • EPSG:27700 - OSGB 1936 / British National Grid

  • EPSG:26915 - NAD83 / UTM Zone 15N


The EPSG code enables the identification of the spatial reference system required in interpreting geographic coordinates.


Without a CRS being defined, the coordinates such as:


40.7128, -74.0060


Would just be mere numbers. GIS software would need to know whether these numbers refer to:


  • Latitudes and longitudes

  • Meters

  • Feet

  • Projective coordinate system

  • Geographic coordinate system

  • Specific geodetic datum


What Does EPSG Stand For?


The EPSG acronym stands for the European Petroleum Survey Group, an entity that created geodetic standards and datasets for oil and gas exploration projects.


These days, the EPSG database is managed by the International Association of Oil & Gas Producers (IOGP) via its geodetic registry.


The phrase EPSG code is now commonly used in the geospatial industry to indicate standardized codes from the EPSG Geodetic Parameter Dataset.


Why Do EPSG Codes Matter in GIS?


EPSG codes are relevant to GIS because GIS data can be properly represented, analyzed, and merged only when coordinate reference systems are known and understood.


Various datasets use various coordinate reference systems. For example:


  • GPS data may use EPSG:4326

  • Drone survey data may use a local UTM projection.

  • Web maps may use EPSG:3857.

  • Country national mapping datasets may use a country-specific projected CRS.


Combining datasets without taking into consideration their coordinate reference systems may result in incorrect data.


Common Problems Caused by Incorrect EPSG Codes


When using incorrect EPSG codes, we have:


  • Data located in the wrong place

  • Layers being offset by hundreds or thousands of meters

  • Inaccurate distance calculations

  • Inaccurate area calculations

  • Misalignment of drone and satellite images with vector layers

  • Inaccurate spatial analysis

  • Web mapping application issues

  • Issues during data transformation


For example, the misuse of geographic coordinates in degrees as projected coordinates in meters will make a dataset completely misplaced.


This is the reason why verification of the EPSG code is one of the main actions that should be taken at the beginning of the GIS process.


EPSG:4326 — The Most Common Geographic CRS


One of the most common coordinate reference systems is:


EPSG:4326


It stands for WGS 84, which is the world geographic coordinate reference system used by many GPS devices.


Its coordinates usually look like this:


Longitude, Latitude


Example:


-74.0060, 40.7128


EPSG:4326 is mainly used for:


  • GPS

  • GeoJSON

  • World datasets

  • Satellite data

  • Location services

  • Geospatial APIs

  • Web applications


Since EPSG:4326 is a geographic coordinate system, its coordinates are in degrees, and not meters or feet.


EPSG Codes and UTM Zones


The Universal Transverse Mercator (UTM) system divides the Earth into 60 longitudinal zones.

Each zone has its own projected coordinate reference system.

For example:

EPSG:32633

represents:

WGS 84 / UTM Zone 33N

Meanwhile:

EPSG:32634

represents:

WGS 84 / UTM Zone 34N

The EPSG code changes because each UTM zone has a different central meridian and coordinate definition.

For WGS 84 UTM zones:

EPSG:32601 to EPSG:32660

are generally used for the Northern Hemisphere, while:

EPSG:32701 to EPSG:32760

are generally used for the Southern Hemisphere.

UTM coordinate systems are commonly used for:

  • Land surveying

  • Drone mapping

  • Engineering projects

  • Topographic mapping

  • Environmental analysis

  • Distance and area calculations


EPSG Codes for Drone Mapping and Photogrammetry


EPSG codes play a significant role in drone surveys and photogrammetry.


The process of drone surveying could consist of the following:


  • Collection of aerial photographs

  • Collection of GNSS coordinates

  • Photogrammetry processing

  • Orthomosaic creation

  • Creation of DSM

  • Creation of DTM

  • Spatial data export


All datasets must have accurate coordinate reference information.


For example, a drone survey might employ:


WGS 84 / UTM zone 43N


while GPS devices would collect worldwide coordinates using the WGS 84 system.


GIS programs should be able to convert the data from one coordinate reference system into another.


In case the incorrect EPSG code is chosen, the resulting orthomosaic, point cloud, and DEM might fail to align with:


  • Property boundaries

  • Existing GIS layers

  • Satellite images

  • Engineering designs

  • Control points of surveying


In the case of professional drone surveys, CRS management becomes a crucial step.


EPSG Codes for Satellite Imagery and Remote Sensing


Coordinate systems are also an important part of satellite imagery.


Various data sets might be provided in various projections.


Examples include:


  • Geographic projection for global satellite images

  • UTM projections for regional data

  • Climate data sets in custom global projections.

  • Polar data sets in polar stereographic projections


GIS practitioners need to ensure:


  • The CRS of the data set

  • The EPSG code

  • The datum used

  • The units of the coordinate system

  • The appropriate transformation


It is especially important when working on:


  • Image classification

  • Change detection

  • NDVI calculations

  • Land cover maps

  • Raster operations

  • Machine learning geospatial analysis

  • Data fusion from multiple sensors


EPSG Codes in Modern GIS Systems


Support for EPSG codes is provided by almost all leading geospatial software tools/libraries, including:



EPSG codes are also frequently used in:


  • GeoJSON pipelines

  • GeoTIFF metadata

  • Cloud-based GIS systems

  • Web map APIs

  • Spatial Databases

  • Drone mapping tools

  • Remote sensing pipelines


Such widespread usage makes EPSG codes one of the key standards in geospatial interoperability.


EPSG stands for an acronym that represents the coordinate reference system of geographic data. The EPSG code is an integral part of the modern-day GIS workflow since accurate spatial analysis relies on proper interpretation of coordinates.


If you deal with GPS data, drone data, satellite imagery, LiDAR data, GIS vector data, GeoTIFF, spatial databases, web maps, etc., knowledge about EPSG codes ensures that your data is accurately located and properly analyzed.


The bottom line here is quite simple – coordinates that lack a proper definition of CRS may result in inaccurate maps and improper analysis. In other words, you need to pay attention to EPSG codes while working with geospatial data.


For GIS practitioners, remote sensing experts, surveyors, software developers, geospatial data scientists, etc., EPSG codes play a crucial role in all stages of GIS workflows.


For more information or any EPSG Code questions, please don't hesitate to contact us at:


Email:


USA (HQ): (720) 702–4849


 
 
 

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