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Chapter 7 Using GIS to Make a Map
mean that the same colors will translate the same way to a printed page or
a photocopy of the printout. It might even have a “washed out” appearance
when the map is projected onto a big screen. Check out Hands-on Application
7.5: ColorBrewer Online to investigate the effect that different color choices
will have on a final map.
How Can GIS Maps Be Exported
and Distributed?
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 printing a copy of the map,
there are several digital formats that maps can be quickly and easily converted
to 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.
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, which becomes important when distributing map data online, as the larger the file, the
more time will be needed to transfer or display the images. For professionalprint-quality maps (such as the maps and graphics in books), the TIFF file format is used at a higher DPI value (such as 300) to create good resolution maps.
To further investigate the impact of color choices on
a map, check out ColorBrewer 2.0, which is available
online at http://colorbrewer2.org. ColorBrewer is a
great tool for color choice and color ramp selection
for a variety of different map data and formats. ColorBrewer 2.0 sets up a pre-determined choropleth map
while allowing you to examine different color selections, see how different color choices on choropleth
maps can be distinguished from one another, or examine the best choices for printing, photocopies, and
color-blind safe schemes. Try out several of the options to determine (based on the pre-set choropleth
maps) what the best color scheme would be. You can
use ColorBrewer in a similar way as Typebrewer—to
determine the optimum setup of colors and then apply those settings to your own maps.
Hands-on Application 7.5
ColorBrewer Online
JPEG the Joint
Photographic Experts
Group image, or graphic
file format.
TIFF the Tagged
Image File Format used
for graphics or images.
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.
Chapter 7 Using GIS to Make a Map
mean that the same colors will translate the same way to a printed page or
a photocopy of the printout. It might even have a “washed out” appearance
when the map is projected onto a big screen. Check out Hands-on Application
7.5: ColorBrewer Online to investigate the effect that different color choices
will have on a final map.
How Can GIS Maps Be Exported
and Distributed?
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 printing a copy of the map,
there are several digital formats that maps can be quickly and easily converted
to 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.
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, which becomes important when distributing map data online, as the larger the file, the
more time will be needed to transfer or display the images. For professionalprint-quality maps (such as the maps and graphics in books), the TIFF file format is used at a higher DPI value (such as 300) to create good resolution maps.
To further investigate the impact of color choices on
a map, check out ColorBrewer 2.0, which is available
online at http://colorbrewer2.org. ColorBrewer is a
great tool for color choice and color ramp selection
for a variety of different map data and formats. ColorBrewer 2.0 sets up a pre-determined choropleth map
while allowing you to examine different color selections, see how different color choices on choropleth
maps can be distinguished from one another, or examine the best choices for printing, photocopies, and
color-blind safe schemes. Try out several of the options to determine (based on the pre-set choropleth
maps) what the best color scheme would be. You can
use ColorBrewer in a similar way as Typebrewer—to
determine the optimum setup of colors and then apply those settings to your own maps.
Hands-on Application 7.5
ColorBrewer Online
JPEG the Joint
Photographic Experts
Group image, or graphic
file format.
TIFF the Tagged
Image File Format used
for graphics or images.
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.