Analysys (Vector) - Completely GIS dan Remote Sensing tutorial - facegis.com
Analysis (Vector)

The ability to perform 'analysis' differentiates GIS from computer assisted mapping (CAD).
Both a GIS and a CAD can store data in layers but a GIS, rather than just displaying different layers, can perform analysis between them, both spatially and via attributes. (refer back to Lecture 1 )


1. Location query

yields attributes of that feature - a database function example attributes


2. Selection by attribute (e.g. where are all the pine stands)

Boolean Logic for queries (named after George Boole, a 19th century mathematician)

  • Boolean function:
  • A type of expression based upon, or reducible to a true or false condition.
  • Logical Operators:
    EQ  Equal
    <>  NE  Not equal
    GT  Greater than
    LT  Less than
    >=  GE  Greater than or equal to
    <=  LE  Less than or equal to
    IN  {1->200}  Between the values of
    CN  ' '  Contains the character string in the quotes

    Example

  • Boolean Operators (to combine items in a table)
    • AND
    • OR
    • NOT
    • XOR ( = either or, but not both)

    These often require the use of brackets to avoid ambiguity in complex queries e.g.

    type = pine AND age > 100 ... selects all old growth pine

    type = pine OR type = fir AND age > 100.. selects any pine OR old growth fir

    type = (pine OR type = fir) AND age > 100 .. selects old growth pine and fir

Examples of boolean logic using Boolean operators: (raster data)

GIS tutorial dan Remote Sensing of facegis.com
Maps A, B, and C represent the original map layers.
The shade areas in D, E, F, and G represent where a condition is met for those locations.
Map D shows :
"Where is condition A but not B met?"
e.g. Which areas have deep soils but NOT spruce?
Map E shows :
"Where are both conditions A and D met?" 
e.g. Which areas have deep soils AND spruce? 
Map F shows :
"Where are either conditions B or C met?"
e.g. Which areas have spruce OR good drainage?
Map G shows :
"Where is condition B or C, but not both, met?"
e.g. Which areas have either spruce OR good drainage but NOT both?

Note: to examine attributes from separate vector data layers, these must frst be overlain (Overlay below)


3. Types of Analysis in GIS 

Commonly used analytical tools in arcgis : append, buffer, clip, dissolve, integrate, intersect, union, erase

a. Database Query
- area, perimeter, values
b. Overlay

overlay: compare different layers and combines attributes: points lines polygons subdivision into new polygons

point and line in area overlay queries area - area overlay queries

union versus intersect union intersect choice of union/intersect

 

c. Algebra
- modify by a given factor: add, subtract, multiply, divide
d. Transform
- modify by projection, datum or geocorrect, clip and erase
e. Classify
- dissolve, append, join, group, merge, generalize
f. Distance
- cost surfaces, distance to features, buffer buffer example
g. Network
- a system of interconnected lines - e.g. hydrological, transportation, utilities, animal migration: network analyst
h. Statistics
- filtering, smoothing, 3D surfacing
i. Modeling

- e.g. fire spread: based on fuel type, wind speed, direction, buffers, topography

Change : change effects, e.g. polar icebeetle spread  fires, volcanoes etc..

 


4. Review

Things you should know after finishing this lecture:
  1. How is a database containing attribute tables essential for most GIS analysis?
  2. Name four general types of analysis in GIS and give specific examples in two
  3. What is meant by a boolean function
  4. List the boolean operators
  5. Why should a 'OR' query yield a larger result than a similar 'AND' query ?

Source: Source: http://www.gis.unbc.ca/courses/geog300/lectures/lect2/index.php