1. Raster Based GIS Analysis

2. Raster Based GIS Analysis

3. What is a RASTER GIS?
A graphic representation of features and attributes
Often looks more like an image than a map
Made of grid cells which contain information
Cells can be any size but are often limited by several criteria

4. Raster GIS represents elements of the real world for analysis:
While feature themes use Coordinates and lines (vectors) to represent geographic features
Raster Grid themes use cells to represent geographic
features

5. Vector GIS We have already used a vector based GIS
It is superb at drawing maps
It is excellent for managing attribute data
It is very efficient for performing calculation along routes and for areas with matching geographies

6. In A Vector GIS... Points, Lines and Areas represent entities
Points - City, Tree
Lines - River, Road
Areas - Forest, Lake
Analysis includes:
Buffering
Intersecting
Network Analysis (shortest path)

7. Raster GIS Very different from the Vector GIS
Uses more images and grids
Stores data differently
Uses square grids to hold data
Uses more “codes” to interpret data
Uses much more processing power
Can generate many more mathematical outputs

8. In A Raster Based GIS... Raster Themes Include: Images Scanned maps,
Air photos,
Satellite images
Grids
DEM, Surfaces

9. In A Raster GIS... Grids represent entities Analysis Includes:
Grids made of cells
Value applied to cell
Analysis Includes:
Buffering/Proximity
Reclassification
Hill-shade/Slope
Interpolation
Surface Calculation

10. Tools for Raster Data Analysis...
Map Algebra
Hill Shades
Slope
Aspect
Raster Modeling
Raster and Vector Integration
Raster to polygon conversion
Contour Generation
Surface Interpolation from point data

11. How does it work? A imaginary grid is placed over an area
Each cell in the grid is given a numeric code for the attribute that is dominant in that cell
Each cell can be...
numeric
qualitative
a feature identifier

12. A Vector to Raster Comparison...
Vector GIS Manages Discrete Features
Distinct boundaries
Stored as integer values
Land use, zoning, vegetation, lakes, roads, rivers
Vector Model
A Raster GIS Manages Continuous Data
Stores data as floating point values
Examples: Elevation, noise pollution, rainfall, slope and temperature
Raster Model

13. The Raster Grid
Raster grids are always square but can be displayed as other shapes
Each group of cells can be considered a layer
Various layers can be overlain on each other
Calculations can be done between layers if the grids line up.

14. Raster Grid Structure Row 1 2 3 Column Cell (2,3)
Grid themes are an organized matrix of cells
Cells are organized into rows and columns
Rows and columns have an index position number
Top left cell is at the 0,0 position
Cells Store a numeric value
Numeric values are codes that represent geographic features
1-Wetlands
2-Water
3-Forest
4-Recreation
Cells with the same value make up a zone
Row 1 2 3
Column
Cell (2,3)

15. Geographic Analysis
Raster systems are superb at analyzing some geography problems such as...
Data that changes continuous over a surface
elevation
vegetation
rainfall
temperature, etc.
There can be used to create new information such as erosion potential.

16. Raster GIS Analysis Questions and answers about something geographic
Leads to decisions that affect people
Involves budgeting money and resources
Spatial query examples
Show me the pine trees
Select the freeway
Spatial analysis examples
Which trees are ready to harvest?
Identify some corridors for the new freeway

17. 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

18. Data Analysis What can we map using GIS (Spatial Analysis Tools)?
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

20. What are the effects of Global Warming?
Land cover and temperature relationships are made clear when the data are seen at once.

21. Will the new building spoil the Park Scenery?
Park planners use GIS to determine if a new Visitor Centre can be seen from the peak.

22. How can I reduce my fertilizer Input?
GIS is used in making crop management decisions to maximize yields and minimize fertilizer input.

23. Managing Raster Data Raster systems are data intensive
they must record data at every cell even if nothing is present
use large amounts of hard drive space
Raster systems have the advantage of being uniformly defined.
This means that very powerful analytical tools can be used with a raster system.

24. Summary Raster systems use grids to store information
Images are raster grids
Images can be given attributes by pixel
Grid can be analyzed for various purposes
Raster data can be overlaid with other grids for greater analysis power.

25. VECTOR! Vector Data Represented by point, line and polygon.
Relatively small file size (small data volume)
Excellent representation of networks.
A large no. of attributes can be attached, hence more information intensive and a number of thematic maps can be prepared from a single layer.
Features are more detailed & accurate.
Creating, cleaning and updating data is more time and labour consuming.

26. Vector con’t
Topology-based analysis & operations are easier to perform (like network analysis etc.).
Can not represent continuous values like land use, elevation etc very well.
Assigning projection and transformations are less time taking and consumes less memory of the computer system.
Topology makes data structure complex.

27. RASTER! Points, line & polygons everything in the form of Pixels.
Large file size.
Networks are not so well represented. Only one pixel value represents each grid cell.
Generalization of features (like boundaries) hence accuracy may decrease.
Simulations and modeling is easier (spatial analysis, terrain modeling etc.).

28. Raster con’t Maintaining is easier.
Excellent for representing data containing continuous values (like land use, elevation etc.)
Coordinate-system transformations take more time and consume a lot of memory.
Grid cells or pixel makes simpler data structure.