How maps are used in GIS

Maps play a special role in GIS:

• They portray logical collections of geographic information as map layers.
• They are at the heart of how GIS is used.
• They provide an effective metaphor for modeling and organizing geographic information as a series of thematic layers.

In addition, interactive GIS maps provide the focal point for using geographic information and bringing that information to life. GIS maps are the way that GIS content is shared among professional GIS users and with everyone online.

This topic provides an important context for the role that maps play in delivering GIS to many new users.

Maps are important, and almost everyone understands and appreciates good maps.

And mapping encompasses a lot—from traditional printed maps and imagery to new media maps that are used on computers, across the Web, and on mobile devices.

A new kind of map is a GIS map, and each GIS map is more than a static map presentation. It is an interactive window into all geographic information and descriptive data, and into rich spatial analysis models created by GIS professionals.

GIS maps are:

• How you communicate and share GIS
• How GIS content is compiled and maintained
• How geographic information is designed and organized using thematic layers
• How you derive new information using geoprocessing and, subsequently, how you visualize, summarize, analyze, compare, and interpret analytic results
• How you share geographic information for use on the Web

Examples of map use

For communication and understanding

Maps are used to communicate and convey overwhelmingly large amounts of information in an organized way. Humans, as spatial thinkers, are able to view a map, associate map locations with real-world phenomena, and perceive and interpret critical information from the sea of content that is contained within each map display.

Maps convey large amounts of information yet still manage to communicate that information effectively and clearly. You can begin to understand and gain insights by using maps.

For finding patterns

Maps are used to discover and investigate patterns such as the characteristics of a population across a city or the movement of antelope between winter and summer habitats. In GIS, many maps can be dynamic and generate reports and views about multiple features and changes across time frames.

Maps visually convey patterns. This map shows the age distribution of populations across parts of Southern California. Darker colors represent areas with older populations. You can click a feature on the map to show the age distribution for the selected block group. In this way, you are using the map as a window into richer sets of geographic and tabular information.

This is a key point. GIS maps provide interactive reports of the information behind the map—not solely lists of attributes but also charts, reports, photos, and virtually any relevant content (for example, a link to a Web site). Defining how features are reported and what you access through a map feature is one of the key specifications that you design and capture when you create a GIS map.

You can also define and capture map interaction properties for time-aware layers as part of your GIS map definition. For example, here is a dynamic map that shows animal movements from GPS tracking devices. You can use the time slider tool to control the display of animal locations on various days. Clicking forward moves to the next day's observations.

Here are four snapshots from a dynamic online map of pronghorn antelope locations from four particular days (out of 300). These dots represent daily movement of pronghorn over a 10-month time span from October 2002 through August 2003. The Time Slider tool in ArcMap is used to put this dynamic map into motion.

For deriving new information using analysis

GIS maps combine powerful visualization with a strong analytic and modeling framework. Analytic models in a GIS are used to generate model results that can be added to your map display as new derived map layers.

Just like you can use each map layer as a window into rich information about features, you can use the map as a window into rich analytic results. You essentially use your GIS map to access analysis models and display their results as a new map layer, which can have the same types of feature reporting, visualization, and animation capabilities that are described above.

A "heat map" showing criminal activity. The hotter colors represent higher crime rates. Image courtesy of the Philadelphia Police Department (http://www.phillypolice.com/).

This map shows predictions for malaria outbreaks in Africa. Darker colors represent a higher projected density of malaria cases. Image courtesy of Adaptation Atlas (http://www.adaptationatlas.org/).

This map illustrates three routes used to optimize travel time between stops for three vehicles in a fleet. Organizations that use network analysis to optimize their vehicle routes typically save 20 percent or more on their annual delivery costs.

Spatial analysis is one of the more interesting and remarkable aspects of GIS. Using spatial analysis, GIS users can combine information from many independent sources and derive an entirely new set of information (results)—applying a large, rich, and sophisticated set of spatial operators. GIS professionals use Geoprocessing to "program their own ideas" in order to derive these analytical results. In turn, these results are applied to a wide variety of problems.

To get status reports

On the Web, maps can be used to communicate status and keep teams up-to-date on events. GIS information is dynamic and, for many layers, is updated on a frequent basis. Dynamic maps are an effective way for everyone to see a common picture of the latest information.

This status map from the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) shows humanitarian response efforts for the Haitian earthquake in January 2010. image courtesy of OCHA (http://ochaonline.un.org/).

A very common application for GIS is the use of operational dashboards that present data feeds and status for a particular set of users. The information layers in dashboards are targeted to a specific audience and their operational needs, enabling them to work more effectively and responsively.

Many Web maps act as operational dashboards that communicate status information across work teams to keep everyone informed and up-to-date. This is an operational dashboard for a water utility. Up-to-the-minute information coming directly from the field, from the operations center, and from the call center is displayed within this operational dashboard.

To compile geographic information

Maps are used to compile and edit features and other data, which are managed and maintained in geodatabases. The best GIS maps for editing present the specific types of features that you want to add to your maps along with the relevant editing tools and attribute properties.

ArcGIS enables users to define and share these editing properties as part of a layer design.

In this map, a feature palette of land-use types is used to lay out land-use zones. You can sketch in (outline) proposed zones for visualizing and analyzing various land-use alternatives.

Mobile GIS maps can be used for collecting data in the field and for receiving and viewing status reports on a mobile map.

To communicate ideas, concepts, plans, and designs

Maps help to communicate ideas, plans, and design alternatives. Effective layer display, combined with interactive feature reporting, provide an important mechanism to visualize, communicate, and understand various alternatives.

Here are a series of 2D and 3D maps that are used to develop and present design alternatives and some of the analysis used as inputs into the design decisions.

To openly share geographic knowledge

As illustrated by these map examples, maps are both effective and efficient for visualizing geographic knowledge. Great maps are how GIS users communicate and how geographic information and knowledge are shared.