The goal of this page is to provide some technical background on the techniques used to display maps digitally, the different types of files used, the advantages and disadvantages of certain types of files and file sizes and how they relate to map files.

File Types: The maps are available as either graphic files (gif or jpg) or Acrobat files:

Acrobat Files: Acrobat files are ideal for maps, they give you the ability to zoom in and out without loss in image quality, perfect for inspecting the details of the maps.

Acrobat files will sometimes look blurry or fuzzy on screen. This distortion is typically only seen on the screen display, the files will print out perfectly. The latest version of Acrobat and Acrobat Reader, version 5.0 has features to reduce this problem. (it will anti-alias vector graphics).

If you have a problem viewing large Acrobat files a more reliable method of viewing the files is to save them to your hard drive first and then open them with Acrobat. This may be accomplished on Windows machines by right-clicking on the link and choosing "Save Target As....".

To view the Acrobat files you must have Acrobat Reader installed on your system. Acrobat software is free and is available for download here:

GIF or JPG Files:  These files are readable in any web browser. These files are more awkward to view than Acrobat files, requiring the viewer to scroll vertically and horizontally when viewing large images (see "File Sizes" below). Zooming in and out is not possible in a web browser as it is with the Acrobat file.

File Sizes: Distributing and displaying maps electronically poses special problems. Maps typically have a lot of detail, often over large areas. This detail typically needs to be present in order for the map to be of any value. A lot of detail over large areas unfortunately leads to large file sizes.

It is possible for us to produce maps with smaller file sizes but the loss of information that is inevitable when reducing file sizes would lead to the loss of utility of the map. The maps on this page have the file sizes are listed next to the links for your convenience.

Viewing large Acrobat files (over 1 meg) over the web may be problematic if you have a slow connection (modem). Problems may include; document fails to load, graphics only partially draw, etc.  Even users with a fast connection may have difficulty viewing these files.  The most reliable method of viewing large Acrobat  files is to save them to your hard drive first and then open them with Acrobat:

This may be accomplished on Windows machines by right-clicking on the link and choosing "Save Target As....". Save the file to your computers hard drive in a location that you will remember.  Open the Acrobat program, find the file that you save to your hard drive in the previous step and open the file just as you would in any other program.

If you have other questions regarding the maps or files on this site please contact: John Cunningham at jcunn@cd.co.contra-costa.ca.us