ArcGIS® is a desktop mapping and spatial data analysis application produced by Esri (formerly, Environmental Systems Research Institute, Inc.). It allows you to create your own maps from scratch starting with geographic data in electronic form and to analyze data that has a locational component. There are also a number of extension applications for specialized analysis.
It is a complex program, so this guide will give a skeletal description of it and will point you in the right directions for more help. Users should be familiar with Microsoft Windows®. Facility with a spreadsheet or statistical package is also useful for cleaning up tabular data or for analyzing it further after exporting from ArcGIS.
ArcGIS uses the concept of a Geographic Information System (GIS) to build maps in which each category of spatial feature is a separate layer. The layers are spatially "registered" so when the user overlays them the program can line them up correctly to build a map. There are several types of layers, and the user has many choices regarding how to depict them. The first three listed are called "vector layers" or "feature layers" and contain individual features that the program can distinguish.
Point (e.g., buildings, landmarks). Zero-dimensional.
Line, or arc (e.g., roads and streets, streams, railroads, power lines). One-dimensional.
Polygon (e.g., political entities, census geographies such as tracts). Two-dimensional.
Raster images (e.g., an aerial photograph, scanned topographic map, or an elevation model). Contrasting with feature-based vector layer, these are images based on an X by Y grid of cells, each of which has a value that represents something like elevation, land use classification, or color value.
Data can be associated with the spatial features, and mapped or analyzed:
There can be attributes, or tabular data, associated with each feature in a layer (e.g., demographic data for each Census Tract).
Data tables (e.g., database or spreadsheet files) can be added ("joined") to a layer if there is a field with common values (e.g., census tract number).
The program can also map spatially referenced data files in some spreadsheet and database formats (e.g, if one field contains latitude/longitude coordinates). Tables that contain address data can be "geocoded" to map the locations based on a street layer. Users can open a non-registered raster image and georeference it using the program's functions, or vectorize features from a raster image.
You can also add your own information to a map with drawing and writing tools.
