First thing you will need to do is make sure that you have Half-Life set to run at 1024 x 768, with developer mode enabled on the command line. I'm going to assume you know how to do these as their pretty basic things that all mappers really should know by now...

Once you have your map up and running, bring down the console, and type in dev_overview 1

The view should change from the standard first-person perspective to a nice birds eye view of the map, with a set of numbers at the top of the screen. These numbers are the important bit...



Now you have the overview displayed, you may need to alter it slightly to fit all the map into one screen, or if your map is quite small, zoom in slightly to fill the screen better. To zoom in and out, use the left and right mouse buttons. You may also need to move the view slightly, and this is simply done with whatever you have your movement keys bound to (usually W, S, A & D).

Bear in mind that your up/down keys will move the map left/right, and your strafe left/right keys will shift it up/down.

Once your happy with the positioning, write down all the numbers from the overview - except for the one marked Z Min, that one isn't needed.

Making sure you don't change any of the positioning of the overview, bring down the console again, and type dev_overview 2. This will simply remove the numbers from the top of the screen so that you can take a clean screenshot of it.

Take a screenshot (usually F5), which should come out like so...(but with your map instead of mine obviously!)



You can quit out of Half-Life now, and find the screenshot you just made. You will need to rename the screenshot so that it has the same name as your map (which will probably simply mean removing a bunch of numbers from the end).

Once that's done, move the screenshot into your overviews folder, which should be residing within the valve folder in your Half-Life directory. Alternatively, if the overview is for a MOD such as Counter-Strike, find the overview folder within its sub-directory (i.e Half-LifeSierracstrikeoverviews).

Create a new text file within the same folder and call it the same name as the map (e.g mapname.txt).

Paste the following text into it...

// overview description file for mapname.bsp

global
{
ZOOM
ORIGIN
ROTATED
}

layer
{
IMAGE "overviews/mapname.bmp"
HEIGHT
}

All you need to do now is add the numbers you wrote down earlier, and change the overviews/mapname.bmp line to reflect the name of your map. I should tell you now that the HEIGHT value is the Z Max value that you wrote down. All the others are pretty intuitive and have the same names as they did on the overview

An example of what I would have made for the overview above would be:

// overview description file for dm_rampart.bsp

global
{
ZOOM 1.33
ORIGIN 1585 -376.00 -690.00
ROTATED 1
}

layer
{
IMAGE "overviews/dm_rampart.bmp"
HEIGHT -1497.00
}

That's it!