DEM File

What are DEM files and how to open them

Are you having problems opening a DEM file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your DEM files.

What is a DEM file?

DEM files have multiple uses, and Build Engine Demo/replay Data is one of them. Read more about the other uses further down the page.

Build Engine Demo/replay Data

Build Engine Demo/replay Data files store recordings of player actions and game events so that gameplay in the Build engine (as used by the 1997 video game Blood) can be replayed exactly as it occurred. Such files are produced when the game is run with recording mode enabled, and are later played back by the same engine and version in order to reproduce input-driven gameplay rather than arbitrary rendered video.

These recordings capture user inputs, network-play states, and game state changes over time. During playback the game engine simulates those inputs step by step, recreates monster behavior, weapon use, and level progression so that the gameplay unfolds identically. The format is versioned; changes to input handling, AI behavior, or weapons between versions of Blood may cause older recordings to misbehave under newer versions because the replay depends on the engine logic being the same.

Internal structure begins with a header that identifies the file as a demo, including the engine version (Blood version, build number), the number of recorded input frames (inputs count), and the number of connected players during recording. After the header comes a sequence of input records - one for each tick or frame - sometimes for each networked player. The header signature is the ASCII characters "DEM" followed by byte 0x1A, appearing at offset zero.

How to open DEM files

Important: Different programs may use files with the DEM file extension for different purposes, so unless you are sure which format your DEM file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested ten different DEM openers which you will find listed below.

Last updated: October 22, 2026

All known file formats using extension .DEM

While Build Engine Demo/replay Data is a popular type of DEM-file, we know of 4 different uses of the .DEM file extension. Different software may use files with the same extension for different types of data.

Half-Life Demo

We know that one DEM format is Half-Life Demo. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

IGO Digital Elevation Map

IGO Digital Elevation Map files store terrain elevation data for use by the iGO GPS navigation engine developed by NNG LLC (formerly Nav N Go). They supply digital terrain relief that adds shaded terrain elevation or coloring to map views, enhancing both 2D and 3D maps in the navigation software. These files enable features like elevation shading in top-down views and terrain detail when navigating in 3D.

The elevation map data is prepared by map vendors and compiled into files that iGO software includes in its "DEM" folder under its content directory (for example /…/iGO/content/dem/ under Android or SD card devices). When active in iGO's settings (e.g. 3d_dem enabled), these .DEM files are loaded to supply only the visual terrain; no elevation values are used by navigation logic or route calculations.

The internal structure starts with an ASCII header "DEMP" at byte offset 0, identifying it as an iGO Digital Elevation Map file.

Vista Digital Elevation Map

Vista Digital Elevation Map is a binary terrain heightmap format created by Virtual Reality Laboratories (the makers of VistaPro) for storing grid‐based elevation (z) data for use in landscape rendering. It captures elevation at equally spaced sample points over a rectangular area, enabling VistaPro to generate realistic relief, shading, and viewpoint effects in terrain visualizations.

Vista Digital Elevation Maps are produced by VistaPro itself, or by auxiliary utilities (for example MakeVista) that convert input z-data or ASCII height fields into the format which VistaPro then uses when loading heightfields. Once created, VistaPro reads these files directly for terrain rendering, lighting, and color mapping. VistaPro offers multiple fixed landscape sizes (for example 258×258, 514×514, 1026×1026 sample grids), corresponding to Small, Large, Huge map sizes.

Internally the file stores signed 16-bit integers (big-endian / "Motorola format") for each grid point in row-major order starting at the south-west corner (lower left), proceeding east across rows, then north to subsequent rows. For example, a Small VistaPro map occupies 133,128 bytes (258×258 values × 2 bytes each). Files of this type begin with the ASCII signature "VistaDEMFile" at offset zero.

Various apps that use files with this extension

These apps are known to open certain types of DEM files. Remember, different programs may use DEM files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about DEM file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.