> For the complete documentation index, see [llms.txt](https://docs.ellipsis-drive.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ellipsis-drive.com/extra/troubleshooting/trouble-with-epsg-or-crs.md).

# EPSG or CRS mismatch issues

#### EPSG or CRS issues during upload

A valid EPSG code is required during upload because it defines how your spatial data relates to real-world coordinates.

Without it, Ellipsis Drive cannot correctly interpret or position your data on the map.

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#### What is a CRS?

A **Coordinate Reference System (CRS)** defines how 2D coordinates in a dataset map to real-world locations on Earth.

It determines:

* how coordinates are interpreted
* how data is projected on a map
* how transformations between coordinate systems are handled

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#### What is an EPSG code?

EPSG codes are standardized identifiers for coordinate reference systems.

They are maintained in a public registry and are widely used across GIS tools and libraries as Spatial Reference System Identifiers.

Each EPSG code represents a specific:

* coordinate system
* projection
* datum
* or transformation rule

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#### Why it matters

Ellipsis Drive uses EPSG codes to ensure:

* correct spatial alignment of your data
* consistent interpretation across systems
* compatibility with GIS tools and web services

Incorrect or missing EPSG information can result in:

* misplaced data on the map
* distorted geometries
* failed uploads

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#### Finding the correct EPSG code

You can look up the correct code for your dataset at:

<https://epsg.io/>

***

{% hint style="warning" %}

### **Important note on projections in Ellipsis Drive**

* Ellipsis Drive visualizes all spatial data in EPSG 4326 by default, regardless of its original projection. Data can be reprojected for visualization in any CRS in external tools such as QGIS or ArcGIS.
* When editing vector data via WFS-T, EPSG 4326 is used as the source CRS to ensure consistent synchronization. Other projections can still be served for visualization, but are not used for transactional edits.
  {% endhint %}