FSX How does FSX Scenery loading mechanism work?

Hey guys,

I really want to know how FSX's scenery loading mechanism works, it includes the following questions:
1. I've seen the 4-digit numbered grid at https://msdn.microsoft.com/en-us/library/cc526966.aspx, but, how FSX finds, with each 4-digit number, the specific relevant files? (bgl, textures)
2. Is the BGL file affects somehow the textures? (Is there some BGL-texture connection?)
3. How is the scenery file (scenery.cfg) connected to the whole thing?; how FSX finds the related textures files?; I mean, where it takes the information from?

The bottom line here is that I wish to understand how FSX maps each texture file to it's correct position in the FSX's world (the specific longitude/latitude and also altitude).

I've searched those questions a lot, but failed to find a decent answer.
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Staff member
Resource contributor
Every BGL has it's location stored in the file header. FSX scans all the files in your scenery cfg locations for their headers before the flight begins. During the flight, the actual BGLs are loaded as needed for the location. I am not sure what is the radius to the current location to trigger the loading and display of the scenery, but I do know the unloading of the BGL (or lack of unloading from memory) is suspected of causing problems in FSX and P3D.

Thank you for your answer, I really appreciate it.

Alright then, it seems my issue with BGL is almost covered now :)

Before we're leaving this 'issue' - what about the textures? (or should I say terrain?, I'm referring here to scenery.cfg & terrain.cfg) - How those three combine together? (bgl, scenery & terrain)
I'll explain myself:
1. The scenery.cfg contains many sections, called by [Area.nnn] (Actually, what is the meaning of 'nnn'?). I guess these sections' purpose is to build up, layer by layer (the user chooses what to include), the FSX's world scenery (Am I right?)
2. Now, let's say Area.001 refers to one BGL file (resides in the scenery directory):
- The BGL file contains it's location (by the way, what is the format of the location?).
- Since the BGL "tells" FSX where it wants to be loaded, I guess that FSX knows also where to load all texture's directory contents - but how it knows how to place each bmp/dds file in it's right position in it's world?
- The last statement leads me to another question: are all textures tightly-connected to the BGL file? i.e., they cannot "exist" without it?
- Actually, if the scenery directory contains multiple BGL files, how FSX separates between each BGL-texture relationship? (If such a relationship do exists..)​
3. Can you elaborate on the terrain.cfg? specifically, what each [Texture.xxx] section means?

My main goal is to download massive land terrain pictures from the internet and load them into FSX's world at run-time. That's why I'm trying so hard to understand this mechanism.
This needs to be done automatically, so there is no place for manual software in this situation.
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I'm familiar with TileProxy, and still, I want to do it. It's a cool project, combines severval areas.
By the way, TileProxy no longer works with google earth.