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

Varieties of geographic Data For a Vector System- 3 basic forms Map or location data -where is it? Attribute data- Information about it Image data- The real world

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 locations Usual to small to be represented by area or polygon Can pinpoint the exact location Eg.Buildings Spot heights Tornadoes Water samples Businesses

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 Province often 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