What is GIS?

"A system of hardware, software, data, people, organizations and institutional arrangements for collecting, storing, analyzing, and disseminating information about areas of the earth." (Dueker & Kjerne, 1989)

"Geographic Information System (GIS): Organized activity by which people measure and represent geographic phenomena then transform these representations into other forms while interacting with social structures." (Nicholas Chrisman, 2003) [click for image]

Different ways to think about GIS:

• As maps (static or dynamic)
• As databases
• As spatial analysis

Levels of measurement

Level	Basic Operations	Examples
Nominal	Level of data measurement that is non comparative, usually representing a description or name	Land-use categories
Ordinal	Determination of greater, less, or equality; ranked data	(good, better, best)
Interval	Determination of equality or difference of interval; addition, subtraction	Temperature in deg C or deg F
Ratio	Determination of equality or difference of ratio; addition, subtraction, division	Distance, mass, precipitation

Common classification methods and how to lie with maps...

Some basics classification methods

• equal interval - each class has the same difference in value
• natural breaks - visual examination, manual determination
• quantile - each class has the same number of units

Example of classification schemes from a student project at Hunter College CUNY

Projections

A map projection is a system by which locations on a curved surface can be displayed on a flat surface. No matter what, there will always be some level of distortion in the angles, areas, directions, shapes or distances.

Types of distortion:

• area - relative areas of mapped projections are not correct
• shape - the shape of a mapped region is not correct
• distance - relative distances between points on the map are not correct
• direction - Compass directions (bearings, azmuths) are not correct

for more information look at Map Projection Overview by Peter H. Dana.

Vector vs Raster

What is vector? - It is an abstraction of the real world in which spatial elements are represented in the form of Points, Lines, and Polygons.

advantages requires less disk storage graphical maps more closely represent hand-drawn topology easier to maintain

disadvantages more complex data structure not as compatible with remotely sensed data overlay analysis is more time consuming than raster data

What is raster? - It is the representation of spatial data as a matrix of cells holding values for an attribute.

advantages simple data structure compatible with remote sensed or scanned data simple spatial analysis procedures

disadvantages boundaries may not be as clearly defined (blocky appearance) projection transformations are more difficult more difficult to represent topology

What makes a good map?

This is a very complex question and we will not discuss much on this topic. However, for our purposes all maps should contain a few basic elements:
a title, the date of creation, source, author, a legend, scale, and a directional arrow (compass rose).

First exercise