Example application:
A consultant has been asked to show how GIS might be used by a fire department. The consultant has already worked on different GIS analyses for this agency, and the time has come to show the benefits to senior management.
"GIS for Emergency Services"was created for the Ventura and Santa Barbara County fire departments by Richard Becker, a geography student at UCSB. It shows how a variety of photographs, maps and diagrams can be used to create a coherent presentation. The software used in this example was Microsoft Power Point and Arc/Info.
The basic steps involved in creating this presentation are:
- Data collection
- GIS analysis
- Presentation design
- Presentation formatting
The first two steps are covered elsewhere in the CCTP detail.
Presentation design involves formulating a plan for communicating ideas to a target audience. In a multi-media presentation such as the example here, that involves coordinating maps and graphics with explanatory text. Increasingly, this means designing presentations to be viewed on the World Wide Web, as well as delivered in person.
While many resources are available for designing general-purpose presentations, such as with Microsoft Power Point, as well as the WWW, this text will focus on the technical steps necessary to get GIS output into a form where it can be used by other software.
Two general principles apply to successful digital presentations: first, they must be easily read by the viewer in a variety of different computing environments. Second, the message they are intended to convey must be equally clear. Conceptual clarity and digital quality go hand in hand.
Background
Data types. There are two basic formats in which graphical data are stored--vector and raster.
Vector data types store elements of a map or display as objects, such as a line or a character. A common vector data type is Postscript, a language developed for printers which specifies each element on a page. Another common type is the Windows metafile, developed by Microsoft for transferring drawings between applications. Other data types include those developed for drawing packages such as Adobe Illustrator and Corel Draw.
The benefit of vector data is that it is easily scalable. Objects that are presented on a small display with a limited number of pixels can be redrawn on a much larger display area with no apparent loss in quality or "pixelization". The disadvantage is that isn't a "picture" of a map, but instead a set of instructions on how to draw it. Thus vector formats aren't viewable in media such as the WWW.
Raster data, however, is a picture of the map or other graphics. The arrangement of cells records the image as it is seen onscreen. Unfortunately, this means that it is not possible to get finer detail by enlarging the image. These bitmaps, however, are the most common way of delivering graphics, especially over the Web.
Since raster data usually contains much redundant information--adjacent pixels are likely to be the same value--they are often compressed to reduce storage space and transmission time. A common storage format is CompuServe's Graphic Interchange Format (GIF). Another, more highly compressed format is the Joint Picture Expert Group's JPEG (or JPG), which is especially appropriate for photographs.
File formats. In the raster domain, files are measured by their pixel count in x and y directions, just like screen sizes on the computer are. The standard VGA screen has 640x480 pixels. They are also measured by their depth, the number of different possible colors for each cell. Sometimes this is expressed as a number, such as 256, or sometimes in bits (the corresponding number is 8 bits).
In practice, these two numbers (640x480 and 256 colors) represent a good lowest common denominator for raster graphics. More pixels or greater color depth is not likely to be supported by all machines, especially in the case of presentation devices such as panel displays and video projectors. If you are currently using a high-resolution display, the output at 640x480 may well look disappointingly coarse. It may be good discipline, however, to use such low resolution, if only to be sure that an audience can see your presentation from the back of the room.
Capture methods. There are two common ways of getting a map from a GIS program. The first is export, and the second is screen capture.
For example, in the widely-used software package ArcView 3, it is possible to export to a variety of vector and raster formats from view and layout documents. If the data is to be reused in a drawing package or presented in a paper document, the most appropriate format is likely to be a placeable Windows metafile (.wmf filename extension)--the Microsoft standard for vector graphics. If, however, the document will be used directly in a web page or other format that requires raster graphics, the best choice is likely to be the Windows bitmap (.bmp).
If it is not possible to use built-in export capability to export graphics, they can still be captured as they appear onscreen. Shareware programs such as SnagIt are available for screen capture on Windows systems.
Since Web browsers such as Netscape don't include support for the .bmp format, those files must be converted to the .gif or .jpeg formats described above. While the most popular program for manipulating these bitmap images is Adobe Photoshop, there are also less expensive shareware programs available, such as Lview Pro, which will do basic file conversion and image processing.
