Simple GIS Data Analysis Flashcards
Spatial Analysis
The process of understanding spatial features/phenomena
Spatial
(absolute location, shape, size)
Feature/feature class, Multi-feature, Local, Regional, Global
Spatial Relationships
Spatial relationship from geometry
Intensity of spatial relationships from attributes
Proximity, containment, overlap
Temporal
Static
Hourly
Daily
Monthly
Yearly
Multi-temporal
(time, duration, frequency)
GIS for Spatial Analysis
GIS provides data, tools, and methods that enable the representation, description, measurement, comparison, understanding relationships, and modeling the past and present of spatial phenomena and prediction of future.
Two Tiers in GIS software systems
Common Tools and Techniques & Extensions or Specialized Tools and Techniques
Common Tools and Techniques
Date query, proximity, overlays
Extensions or Specialized Tools and Techniques
Terrain mapping and analysis, path analysis and network applications
Single Layer Analysis
how close each other, how different from each other in pattern land use classification
Multi-layer Analysis
change detection –> pre & post desaster,spatial model –> Universal Soil Loss Equation (USLE)
Integrated Analysis
both spatial and attribute data
involves attributes, location and topology
Analysis involves
Analysis involve selection, measure and classification, overlay, surface operations, analysis of spatial connectivity……
Attribute Data Query
Attribute data query retrieves a data subset by working with attribute data
The selected data subset can also be saved for further processing
Selected Data Subset Can Be Simultaneously
examined in a spreadsheet lile data table structure (records and fields)
displayed in charts/ graphs, and
Can be linked to the highlighted features in a map
Selection of attribute data or the data query requires an expression
must be interpretable by the GIS DBMS
varies from one system to another
ArcGIS uses SQL (Standard Query Language) for query expressions
SQL (Structured Query Language)
designed for relational databases, by IBM in the 1970s, and used by many commercial database management systems
The basic syntax of SQL includes the following:
select [ selects fields as a list]
from [name of the table of the database]
Where [specify the selection criteria]
Query Expressions
Query expressions consist of Boolean expressions and connectors
A simple Boolean expression contains two operands and a logical operator
Boolean connectors are AND, OR, XOR, and NOT are used in query functions and overlay operations.
Connect two or more expressions in a query statement.
NOT, AND, and OR are actually used in the operations of Complement, Intersect, and Union on sets in probability
E.g.:
Parcel. PIN = ‘P101’
Boolean Connectors
Not
The blue shaded portion represents the complement of data subset B contains elements of the set A that do NOT belong to B
Boolean Connectors
OR
The union of data subsets A and B the set of elements that belongs to A OR B
Boolean Connectors
AND
The intersection of A and B –> the set of elements that belongs to both A AND B
SQL (Structured Query Language)Use of Boolean connectors
PIN relates the owner and the parcel tables and allows use of SQL with both tables
Spatial Data Query
…refers to the process of retrieving a data subset from a layer by working directly with features
Select Features
Select features using a cursor, a graphic, or the spatial relationship between features
Spatial Relationships
Spatial relationships used for query include containment, intersect, and proximity
Feature Selection by Graphic
Uses a graphic, such as a circle, box, line or polygon to select features that fall inside or are intersected by the graphic
Feature Selection by Spatial Relationship
Select features based on their spatial relationship to other features
In the same layer or in different layers
Containment, intersect, proximity
Containment
Select features that fall completely within features for selection,
Intersect
Select features that intersect other features
Proximity
Select Features within a specified distance of other features
Combining Attributes and Spatial Data Queries
When data exploration requires both attribute and spatial query
E.g.: Gas stations within one mile of freeway exits and have an annual revenue exceeding a million dollar
Vector Data Analysis
Vector data analysis uses the geometric objects
point, line, and polygon
Accuracy Of Analysis
Depends on the accuracy of these objects in terms of location and shape.
Topology is an important factor for some vector data analysis such as
Buffering and overlay
Buffering
is based on the concept of proximity
is a single layer operation
Buffering creates two areas
within a specified distance of selected features–>buffer zone
the other area that is beyond the buffer zone
Several variations in buffering:
boundaries of buffer zones may remain intact so that each buffer zone is a separate polygon
Applications of Buffering
City ordinance: no liquor store within 1 Km of school
Two-mile buffer along streams to minimize sedimentation from logging
Forest restrict oil & gas drilling within 500 feet of roads
Stream buffers to protect streams from agriculture or construction
An area of spatial proximity around a point refers to which GIS operation?
Buffer
Which of the following queries will select all housing parcels classified as “residential” (from a layer called PARCELS) that are also considered to be “seasonal” homes (from a layer called STATUS)?
PARCELS = “residential” AND STATUS = “seasonal”
Methods of Overlay in Vector Data
Relationship
Containment and overlaps
Multi-layer operation
layer must be spatially registered
based on same coordinate system
An important consideration in a overlay operation is the …
feature types
Two Groups of Methods of Overlay in Vector Data
Uses two polygon feature layers
Uses one polygon feature layer and the other point or polyline-feature layers
Understanding Overlay
Combines the geometries and attributes of two feature layers to create a single output layer with a modified set of attribute table.
Each feature on the output contains a combination of attributes from the input layers
Overlay in Vector data
Based on the type of layers the combination the relationship approaches can be
-polygon-on-polygon, point-in-polygon, line-in-polygon
Vector Data input and output in overlay
Always uses polygon as the overlay theme
Output is the same as the input
Vector data overlay: How it works
Lines are split at polygon boundaries
Lines take on attributes of overlapping polygons
Overlay Boolean Operators
AND
Results in “true” for all areas that meet both the first and the second criterion
Overlay Boolean Operators
OR
Results in “true” for all areas that meet either the first or the second criterion, independent on the areas overlapping or not. In other words, at least one criterion has to be true.
Overlay Boolean Operators
XOR
Results in “true” for all areas that meet either the firs tor the second criterion but not both
Overlay Boolean Operators
NOT
Results in “true” for all areas that meet the first criterion but not the second
GIS Terms in Overlay Methods
Methods may name differently in different GIS package, however, they are based on the Boolean connectors
- AND, OR, and XOR
GIS TERMS:
Intersect
If it uses the AND connector
GIS TERMS:
Union
If it uses the OR connector
GIS TERMS:
Symmetrical Difference or Difference
If uses the XOR connector
GIS TERMS:
Identity or Minus
A minus B
Other methods for data selection
You can use SQL for spatial data selection and extraction through attribute data
Spatial Tools for Spatial Data Extractions
Dissolve, Clip, Update, Erase, Eliminate, Append, Split
Dissolve
Removes boundaries between polygons or nodes between arcs
Features with same attributes are dissolved
Identical to spatial merge
Update
All features exist in output
“Under-lapping” features from input layer are erased
Attributes only from input theme exist in output
Order of input layer and overlay layer is important
Polygon on polygon only
Clip
Cookie cutter”
Only input theme features and attributes exist in output
Polygon on polygon, line, or point
Erase
Only input theme features and attributes exist in output
Order of input and overlay matters
Polygon on polygon, line, or point
Eliminate
It merges the selected polygons with neighbouring polygons keeping the largest shared border or the largest area
“Eliminate” is used most often to remove sliver polygons created in an overlay of two layers
Append
Append combines features from two or more layers into a single output layer
It does not calculate new topological relationships between the resulting features.
Split
Split creates output layer by overlaying two sets of features.
Split performs a series of Clip operations, one for each output layer.
Each output layer contains only those portions of input layer features that are overlapped by the specified polygons of the Split Layer.
Raster DATA Model
a regular grid to cover space
value in each cell represents a characteristic
Raster Data Analysis
Popular use in application model
Various type of raster data (GRID, DEM, DRG…)
Software package defines what type raster data can be analyzed required conversion
large variety of analysis operations
Algebraic operations for Raster Analysis
output is a single layer
Statistics (max, min, range, mean, median, mode, sd..) of the input layers cell values to the output layer
Majority, minority, or unique value of the input layers cell-values to the output layer
Multi-layer analyses are Similar to the vector overlay operations
AKA Map Algebra
Algebraic Operations in
A single layer
or
Multiple raster layers
Suppose you have two layers of data and you want a new layer that shows everything in all four of those layers. Which type of overlay operation would you use?
Union
If you create a 1-mile buffer around a single point, the shape of the buffer will be:
A circle
Spatio-temporal
(changes in a spatial description over time, example change of extent)
Non-spatial (name, owner, quality, color, …………)
name, owner, quality, color
Non-spatio-temporal
(changes in a non-spatial descriptions over time, example change of colors
