> ## Knowledge Base Index
> Fetch the complete knowledge base index at: https://faq.geovelo.app/sitemap.xml
> Use this file to discover available pages before exploring further.
> Pure-Markdown content can be obtained by appending a '.md' suffix to the content URLs listed in the sitemap (without the trailing slash).

# How does Geovelo calculate altitude differences?

### What data does Geovelo use to calculate elevations?

To define the elevation profile of a route, Geovelo uses data from two suppliers: 

- on a global scale: data from NASA's Shuttle Radar Topography Mission (SRTM), 
- on a local scale: data from Digital Terrain Models (DTM). 

The data are then pooled with those from OpenStreetMap. 


#### Why do Geovelo's elevation profiles not necessarily correspond to reality?

Profiles are calculated from altitudes, which are themselves more or less precise. 

| Altitude accuracy can vary from a few centimeters (50 cm in planimetry, 15 cm in altimetry) for local DTM models, to several tens of meters (20m in planimetry, 16m in altimetry) for SRTM. 


#### Why are vertical drops recalculated after a trace?

The final vertical drop that appears in the statistics is defined by your phone's GPS data in addition to Shuttle Radar Topography Mission (SRTM) data. 

#### The meaning of colors

Here's what the colors in your graph mean. You can also display them at any speed by extending the arrow.


![](https://storage.crisp.chat/users/helpdesk/website/ab9f34b0934a4800/image_1uissfk.png)