"Experience is one thing you can't get for nothing"

                                                                                                                                                    Oscar Wilde
 

A Geographic Information System (GIS) is a set of coded geographical analytical toolsused to store, analyze and visualize any kind of spatial data referenced to a specific coordinate system. The main technical functions of GIS include:
 

• overlay of spatial data, creation of statistics and summary of spatial variables;
• integration of data with different scales and coordinate systems;
• creation of new information via data integration.

Prior to computer age, geographic information systems existed as geographic analytical knowledge preserved in manually­produced maps with different layers of information. Maps could be produced that performed all the functions associated with modern GIS, but the manual interpolation of data, conversion of units and coordinate systems that made this possible required enormous human resources. Pre­computer maps had the additional disadvantage of being simultaneously  maps  and  data . Map legends explained the methods used and the data s origin, but no independent analysis of the data was possible.

The development of GIS has resulted in the separation of maps and data. In GIS, data arenot maps, and in fact do not have to be  visible  until they become necessary to the user. Spatial data analysis can be done without visual display of the data as soon as the data are verified and properly prepared. Because they are separated from data files, maps can be modified easily in an electronic environment using software functions. Caution must be exercised, however, in the application of the software and in the use of final hard copy maps.

GIS software :

There are many kinds of software packages produced for GIS purposes, all of which are generally referred to as  GIS software . They include graphical, statistical and database management tools. The complexity and power of these tools defines how comprehensive a particular GIS software package is.
 

• data analysis tools;
• data management tools, including input and output;
• data visualization tools.

Depending on the software type these modules can be accessed by the user via:
 

• commands (typing at the prompt);
• separate menues, buttons and "clickable" icons;
• separate modules, having combination of menues, buttons and "clickable" icons;

Various software packages (shareware and commercial) are available for review via theInternet or in specialized journals and GIS publications. GIS modules can be found within remote sensing software packages.

For the class, the main GIS software package is Arcview 3, developed by ESRI, Inc. The supplemental package will be ARCINFO, also developed by ESRI. ARCINFO has command­ driven modules (and also some customized menu­driven tools) and can be used as a programming language to develop customized GIS applications. Arcview 3 is a modular software package in which all manipulations are controlled by menus, buttons and  clickable  icons or tools. It also has the programming language Avenue, which allows the user to modify the Arcview interface and create customized applications. Both software packages use and create so­called  coverage  and  shapefile  GIS formats. They can also import and export formats used by other software types (see relevant documentation and description on the ESRI Web site).

ARCINFO software will be used in the class to demonstrate principles of digitizing and topology creation. Arcview will be used for the majority of class projects.

One of the remarkable features of Arcview is its ability to include external modules in the software, so­called  extensions . These modules exist both as shareware (i.e., written by GIS  gurus ) and commercial (i.e., licensed) software. Free extensions are available via the ESRI site, while licensed extensions have to be bought. One such extension will be used in class. It is called  Spatial Analyst , and will be used to create digital elevation models, terrain analysis, and hydrological and hydrogeological modeling. It also contains interpolation functions and tools to manipulate grids­­raster GIS data.

What is "GIS format" ?

GIS format is any digital georeferenced file that allows the user to apply various geographical analytical tools, such as interpolation, distance measurements or data visualization. Usually, the GIS file must have, at a minimum:
 

• a coordinate pair;
• an identification number (index);
• an attribute.

This general definition of GIS format is preserved in various GIS software packages­­ ARCINFO, ARCVIEW, MAPINFO, GRASS, IDRISI, etc.

GIS data formats are usually referred to as  coverage ,  shapefile ,  Digital Exchange File (DXF) , etc.

Do not mix GIS data formats with digital ready­for­printing files containing maps (e.g.,Encapsulated Postscript File (EPS), RTF, JPEG, TIFF, GIF)!
 

GIS Hardware and Peripheral Devices:
 

• Computing Processing Unit (CPU), Monitor;
• Printers, Plotters;
• Scanners, Digitizing Tablets;
• Data storage devices;
• Back­up system (tape driver, CD­ROM).

Main Geographic Elements in GIS:
 

• Scale
• Map Projections/Coordinate systems

EXAMPLES OF GIS APPLICATIONS:

  Cave Man & GIS

  Map Production

  Urban Growth Modeling

  Emergency Response