Global Image Archive

Welcome to the Global Image Archive

    What is a World File?

      A World File is a small reference file containing necessary information a GIS (Geographic Information
      System) or other similar software package requires in order to reference the images to real world
      coordinates. By placing the World File in the same folder as the image (which shares the same root
      name but different file extension) the software is able to read the information contained in the file as it
      loads the image so it can be placed in its correct location. If you are using a .jpg image the world file
      will carry the .jpgw (or .jgw) extension and if you are using a .tif image the accompanying world file will
      have a .tifw or .tfw extension.

      Because these datasets originate from different sources slight geographic adjustments may be
      requited if you wish to integrate them with each other or with additional data. The world file allows
      you too spatially adjust the image by changing the last two lines of the text. This adjustment can be
      performed using a text editor like Notepad. To shift the image in an east or west direction adjust the
      value in line 5. To shift the images in a north or south direction adjust the value in line 6. When you
      save the world file make sure it maintains the world file extension and not a .txt extension which is the
      default for Notepad.

      If your software package doesn’t recognize a .jpgw file you could try converting the .jpg image to a .tif
      image in an image processing software package like Photoshop and then rename the world file
      with a .tifw or .tfw extension.

        Contents of a World File:
        Line 1: Size of each pixel in the X (horizontal) direction (in map units)
        Line 2: Rotation term for row
        Line 3: Rotation term for column
        Line 4: Size of each pixel in the Y (vertical) direction (in map units)
        Line 5: X coordinate of the center of the upper left pixel
        Line 6: Y coordinate of the center of the upper left pixel

The author provides this data as a public service and is not responsible for
any problems relating to accuracy, content, design, and how it is used.

Compiled by: Paul Illsley