A Quick Introduction to GIS

What is GIS?

Definition: Analysis that combine relational databases with spatial interpretation and outputs often in form of maps. A more elaborate definition is that of computer programs for capturing, storing, checking, integrating, analyzing and displaying data about the earth that is spatially referenced.

A GIS Map Contains Layers• A GIS map is made up of layers, or

collections of geographic objects that are alike.

• To make a map, you can add as many layers as you like.

Layers Contain Features or Surfaces

• Each geographic object in a layer --- each city, river, lake, or country --- is called a feature.

• Not all layers contain features. A single continuous expanse that changes from one location to another is called a surface.

Features Have Shape and Size

• Features can be represented as one of three geometric forms:– A polygon– A line– A point

• This kind of data is called vector data.

Surfaces have Numeric Values Rather that Shapes

• Surfaces have measurable values for any particular location on the earth

• This is raster data—a matrix of identically sized cells where each cell contains a measurement for that location.

Features Have Location

• GIS uses a coordinate system to associate features with location

• These coordinate systems make use of Geodetic datums

Features can be Displayed at Different Sizes

• Zoom and out changes the scale of the map

• Scale is the relationship between the size of the features on the map and their size in the physical world.

Features are Linked to Information• Information about the features in a layer is

stored in a table.• The table has a row for each feature and

the columns values are attributes of that feature

Tables• The links between features and their

attributes makes it possible to query and display the results on the map.

Thematic Maps• You can use attributes to create thematic

maps---maps in which colors (or other symbols) are used to indicate attribute values.

Features have Spatial Relationships

• You can also ask questions about spatial relationship among features.

• GIS uses coordinate information to compare locations

You can Create New Features• GIS can look for areas of overlap between

features of different layers and create new features to identify these areas.

ArcMap and ArcCatalog

ArcMap is the application for making maps and analyzing data.

ArcCatalog is the data management Application.