JPEG the Joint Photographic Experts Group image, or graphic file format
TIFF the Tagged Image File Format used for graphics or images
Once a map has been designed and formatted the way you want it, it’s time to share and distribute the results. Rather than just print a copy of the map, there are several digital formats to which maps can be quickly and easily converted for ease of distribution. A simple way is to export the map as a graphical raster file—this saves a “snapshot” of the map as a digital graphic that can be viewed like a picture, either as a file or an image placed on a Website. There are many different formats for map export, and two common ones are JPEG (Joint Photographic Experts Group) and TIFF (Tagged Image File Format). Images saved in JPEG format can experience some data loss due to the file compression involved with JPEGs. Consequently, JPEG images usually have smaller file sizes for viewing or downloading. Images saved in TIFF format have a much larger file size but are a good choice for clearer graphics.
DPI dots per inch—a measure of how coarse (lower values) or sharp (higher values) an image or map resolution will be when exported to a graphical format
The clarity of an image is a function of what DPI (dots per inch) setting is used when the map is exported to a graphic. The lower the value of DPI (such as a value of 72), the less clarity the resultant image will have. Very low values of DPI will result in the exported image being very blocky or pixilated. Maps exported with higher values of DPI (such as 300) will be very crisp and clear. However, the higher the DPI value, the larger the file size will be—and this becomes important when you’re distributing map data online, as the larger the file is, the more time will be needed to transfer or display the images. For professional-print-quality maps, the TIFF file format is used at a higher DPI value (such as 300) to create good resolution maps.
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GeoPDF a format that allows maps to be exported to a PDF format, yet contain geographic information or multiple layers
A GeoPDF is another option for exporting and distributing maps. A GeoPDF allows the user to export a GIS map in the commonly used PDF file format, which can be opened by the free Adobe Reader software using a special free plug-in. A GeoPDF differs from a regular PDF in that it allows the user to interact with map layers and get information about the coordinates of locations shown in the PDF. For instance, a GeoPDF could contain multiple layers of data that the user could turn on and off (such as annotation for road names or a separate layer of the roads themselves) as in GIS (see Chapter 13 for more usages of GeoPDFs with other maps).