Geographic Information Systems

Data Analysis

What is GIS Data ?

Types of GIS Systems

Raster• Features

represented as a matrix of cells over continuous space

• Each layer is one attribute

• Analysis is done by combining layers to create new layers with new values

• Cell size is critical

Vector• Each feature is a row

in a table• Define by specific

X,Y locations coordinates in space.(lat,long)

• Features can be discreet locations or events (trees or Earthquakes)

• Not as memory intensive

Raster Data• Grids represent entities

– Grids made of cells– Value applied to cell– Each grid represents one attribute– Continuous surface of a matrix of cells

• Analysis Includes:Analysis is done by combining layers to create a new layer with new cell values– Buffering/Proximity– Reclassification– Hill-shade/Slope– Interpolation– Surface Calculation

Vector (Feature) Data

• Points, Lines and Areas represent entities

– Points - City, Tree– Lines - River, Road– Areas - Forest, Lake

• Analysis includes:

– Buffering– Intersecting– Network Analysis (shortest path)

Point Data

Points represent objects that have discrete locationsUsual to small to be represented by area or polygonCan pinpoint the exact locationEg. Buildings

Spot heightsTornadoesWater samplesBusinesses

Line Data

Represent objects that have length but are too narrow to be shown as polygons

Can be broken into many segments known as ARCs

• Eg.-rivers – Roads – Railways– Bridges

Area or Polygon Data

• Defined by borders and are closed• Usually to large to be depicted as points or

lines• Can be legally defined – building lots• Administrative- countries or

counties• Naturally occurring boundaries- Ecozones

Lakes

Coordinate Systems

• A coordinate system is required to reference data to a real world location. It could be lat/long or military grid.

• ArcView transforms the image coordinates into real-world x,y coordinates. – Vector data sources stored in a real-world x,y

coordinate system. – Images/Grids stored in rows and columns of pixels-– Pixel size (resolution) is critical

• ArcView looks for georeferencing information stored with the image.

Attribute data

• The descriptive data that a GIS links to map features

• Attribute data is collected and compiled to link to specific locational data-

census data by Provinceoften comes packaged with

map data

Image Data

Data produced by an optical or electronic device. Usually originally in Raster format

Remote sensed data– Satellite & remote sensed Data– Aerial photography – Scanned data– Photographs

• Can be linked to locational data or registered to display with other themes and layers with real world coordinates

What is GIS Analysis

• From simple to Complex• Simple - Sometimes by just making

a map you are doing analysis• Complex - Sometimes we use

many layers of data to simulate real world events

Data Analysis

What do we Map in a GIS?

•Map where things are-Location Analysis•Map the most and least-Quantitative

Analysis•Map concentrations- Density•Map what is inside-Monitoring•Map what is nearby-Relationships•Map Change-Prediction