2. Raster and Vector
2 Major GIS Data Models

3. Data Models: Represent real world in Digital Form
Raster:
- divides entire study area into a
regular grid of cell in a regular sequence
- Each cell = single value
- Space filling: every location in study area
corresponds to a cell. Shows what occurs everywhere
- one set of cells & associated values = layer
Vector:
- uses discrete line segments or points to identify locations
- Objects such streams or boundaries are formed by
connecting line segments
- Objects do not necessarily fill space.
Shows where everything occurs.
- one set of points, lines, or polygons = layer

4. A. B. C. Creating a Raster: Features in the “real world”
Grid is placed over ‘real world” features
The smaller the grid, the more accurate the map &
the larger the data storage or file size
Each block is a cell B.
Each cell is assigned a value
Automated methods used to enter data
Satellite image such LANDSAT contains
7.4 million cells
Raster data can be compressed C. 2 2 2 2 2 2 2 2 2

5. Classes of Raster Data Values
Multiple layers with cell values can be overlayed
Can add or subtract layers
Resampling may be needed in order to allow cells
from different layers coincide.
Remote sensing or satellite photos interfaces best
with raster since images can be transferred to cell
values using automated methods

6. Conversion between data structures: Vector to Raster
Raster to Vector

7. Topology: Mathematical method used to define spatial relationships
between points, lines, and polygons

8. Topology Use in GIS x, y coordinate or location Adjacency Containment
Connectivity

9. Topology is required to determine spatial relationships in a GIS

10. With or without Topology:
Computer software can NOT see features as
humans do:
Humans see implicitly
In GIS, features must be defined explicitly

11. Topology uses points, lines, & polygons
(0D, 1D, & 2D)
to explicitly define spatial relationships
Lower dimensional objects build higher
dimensional objects:
points-> lines-> polygons

12. Topology Importance:
Spatial Analysis- allows GIS to perform spatial queries.
ie. Point in polygon, buffering , network analysis, polygon overlay
Processing Speed- is faster since relationships are defined
Data Storage- less data is required to be stored; thus allows smaller files
ie. Polygon A & B share same polyline, thus need to store only once

13. Map Design and Components

14. Attributes of GOOD Map Design:
Clarity
Balance
Figure-ground
Hierarchical Organization
Color
Pattern
Lettering

15. Clarity: Point, line, & polygon symbols as well as text must clear & readable
Lines- clean, sharp, uniform
Shapes- symbols & shading are distinguishable
Text- legible

16. Balance: proper arrangement of
component parts of map (title,legend,
map body)
3 to 5 ratio pleasing to eye
Figure-ground:
figure- portion of map that is being
portrayed
ground- formless area or background

17. Hierarchical Organization:
To show levels of relative importance or comparisons on the map.
Can be shown with point, line, or polygon objects

18. Color: by choosing one hue (one color range) can look at map to
distinguish different objects or interpret hierarchy

19. Patterns: by choosing patterns that are increasing dense patterns, you
can look at map and interpret hierarchy (without reading the legend)

20. Lettering: Text position and orientation rules to follow
(Remember these are guidelines; sometimes rules must be broken)
Point objects: same font size & positioned horizontally above , below, left, or right
Do not split text by other objects
Line Objects: text should run parallel to the feature (ie. road or river)
if text must follow vertical feature, it is easier to read going
up on left (of line) or down on right.
Polygon Objects: Text should be within boundary. Text should be horizontal
if at all possible. If text must be tilted, curve the text.

21. Bad Lettering
Good Lettering

22. Components of a Map: Title: Subject matter, date of data, &
by what geography
North arrow (optional)
Map body
Legend: explain symbols,
color, patterns used.
For thematic legends:
Legend title = UNITS used,
Ascending or descending
order
Scalebar (optional)
Source: Who, what, when
Prepared by: who, include date
prepared