A CID file is a chart description file created by Navigator, a celestial navigation program. It contains information about a .GIF, .JPG, or .BMP chart image. CID files include the name of the associated chart image, description of the file, reference points that define the image pixels, an image MD5 digital signature, and limits of the charge.

Raster chart images typically come from scans of paper charts that are saved in the GIF, JPEG, or BMP format. Users can then import the GIF, JPG, or BMP file into Navigator with the ChartMaker tool that comes with Navigator. The CID file is created when the raster chart image is imported and is used to store information about the raster chart, which is then used by Navigator to display the chart to the user.