Geospatial Tools and

Techniques

Azimuth (degrees east of north)

and Airport use:

Vocabulary Activity

• Polygon •••• Altitude

• Line •••• Topography

• Prime Meridian •••• Demographic

• Latitude •••• Economics

Vocabulary Activity

• Spatial •••• Longitude

• Analysis •••• Equator

• Point •••• Azimuth

What is GIS?

• Geographic Information Systems

GIS--What is it?No easy answer anymore!

• Geographic/Geospatial Information

– information about places on the earth’s surface

– knowledge about “what is where when”

(Don’t forget time!)

– Geographic/geospatial: synonymous

• GIS--what’s in the S?

– Systems: the technology

– Science: the concepts and theory

– Studies: the societal context

Geographic Information Technologies• Global Positioning Systems (GPS)

– a system of earth-orbiting satellites which can provide precise (100 meter to sub-cm.) location on the earth’s surface (in lat/long coordinates or equiv.)

• Remote Sensing (RS)

– use of satellites or aircraft to capture information about the earth’s surface

– Digital ortho images a key product (map accurate digital photos)

• Geographic Information Systems (GIS)

– Software systems with capability for input, storage, manipulation/analysis and output/display of geographic (spatial) information

GPS and RS are sources of input data for a GIS.

A GIS provides for storing and manipulating GPS and RS data.

Decision

GIS ProcessOutput

GIS

analysis

Import or

build datasets

Define GIS

criteria

Define

problemDecision

GIS ProcessOutput

GIS

analysis

Import or

build datasets

Define GIS

criteria

Define

problem

Geographic Information

Systems

Simply said:

Geographic » maps

Information » data

System » digital

A GIS links information to geographic location

(connects the what to the where), allowing you to

seek patterns and relationships that may not

otherwise be apparent.

So, each layer contains 2 kinds of data that

leads to information:

• Spatial data -> information –location and shape of the geographic features

• Attribute data -> information –other characteristics of the features

A layer serves as a shortcut to the data. It also tells ArcMap how the data should be drawn.

Spatial and Attribute Data that

Leads to Information• Spatial data (where)

– specifies location

– stored in a shape file, geodatabase or similar geographic file

• Attribute (descriptive) data (what, how much, when)

– specifies characteristics at that location, natural or human-created

– stored in a data base table

GIS systems traditionally maintain spatial and attribute data separately, then “join” them for display or analysis

– for example, in ArcMap, the Attributes of … table is used to link a shapefile (spatial structure) with a data base tablecontaining attribute information in order to display the attribute data spatially on a map

THREE SPATIAL

COMPONENTS

• Point

• Line

• Polygon

Two Basic GIS Data Models

• Vector GIS

– Represent space with points, lines, and polygons

– One spatial feature, many attributes

– Does not fill space

– Relatively intuitive visualization – maps

• Raster GIS

– Represents space with uniform cells on a grid

– One cell, one attribute

– Fills space

– Visualization not as intuitive – can look very odd

Representing Data with Raster and Vector Models

Raster Model

• area is covered by grid with (usually) equal-sized, square cells

• attributes are recorded by assigning each cell a single value based on the majority feature (attribute) in the cell, such as land use type.

• Image data is a special case of raster data in which the “attribute” is a reflectance value from the geomagnetic spectrum

– cells in image data often called pixels (picture elements)

• Vector Model

The fundamental concept of vector GIS is that all geographic features in the real work can be represented either as:

• points or dots (nodes): trees, poles, fire plugs, airports, cities

• lines (arcs): streams, streets, sewers,

• areas (polygons): land parcels, cities, counties, forest, rock type

Because representation depends on shape, ArcView refers to files containing vector data as shapefiles

0 1 2 3 4 5 6 7 8 9

0 R T

1 R T

2 H R

3 R

4 R R

5 R

6 R T T H

7 R T T

8 R

9 R

Real World

Vector RepresentationRaster Representation

Concept of

Vector and Raster

line

polygon

point

Representing Spatial Elements

• RASTER

• VECTOR

• Real World

Vector or Raster?

Vector or Raster?