Some drawing systems output maps in jpg format rather than bmp (bitmap) format. NoiseMap can't read jpg format, but you can easily convert the maps to bmp. I open them in Adobe Photoshop elements and then save them as .bmp (bitmap) files.
I don't rescale or do anything - I just select BMP from the format drop-down in Photoshop Elements, and select Windows 24-bit format.
The jgw file is a 'world file' format which tells the mapping software where to locate the map in Ordnance survey co-ordinates. To use it in NoiseMap, change the file extension to bpw and it will now work with the bitmap that you created. When you ask NoiseMap to open the bitmap, it will tell you that the bpw 'calibration' file is present and ask if you want to use it. Say yes and the bitmap will open at the correct scale and location.
