Spatial Analysis and Modeling

GEO 442

1. What is Analysis?

• The process of identifying a research question

• Modeling that question • Investigating model results• Interpreting the results

2. What is Spatial Analysis?

• Same process but with spatial data

• Example: Topological overlayAn analysis procedure for determining

the spatial coincidence of geographic features

3. What is modeling?

• A representation of reality used to – simulate a process– understand a situation– predict an outcome– analyze a problem

• A model is structured as a set of rules and procedures

4. What is Spatial Modeling?

Use geographic data to; describe, simulate, or predict real-world problems or systems.

3 categories of spatial modeling

• these can be applied to geographic features within a GIS:– geometric models, distance between

features, generating buffers, calculating areas and perimeters

– coincidence models, such as topological overlay

– adjacency models (pathfinding, redistricting, and allocation)

5. Two spatial models for storing geographic data

• Raster data model - matrix of square cells• Vector data model - data stored as

coordinates.

• Similar, represent a layer or set of geographic features like points, lines, and polygons.

• Different in the way they model or represent spatial data.

Vector data model• Point, line and polygon objects on a map are stored as

as a collection of x and y coordinate pairs in a table. • The x and y coordinates represent the point’s distance

from an origin point.

• Points stored as a single pair of x and y coordinates • Lines, store the x and y coordinates of the beginning

point (from node) of the line and the end point (to node) of the line.

• Curves or changes in direction - series of x,y coordinate pairs, (vertices), at each direction change between the beginning point and end point of the line.

• Area (polygon) - enclose it with a line, making the beginning and ending points of the line equal.

• Polygons which share a boundary are called adjacent.

The diagram below shows how real-world objects can be represented on a computer monitor by x,y coordinates.

The coordinate pairs 1,5 3,5 5,7 8,8 and 11,7 represent a line

(road) The coordinate pairs 6,5 7,4 9,5 11,3 8,2 5,3 and 6,5 represent a

polygon (lake). The first and last coordinates of the polygon are the same; a

polygon always closes.

To keep track of many features, each is assigned a unique identification number or tag.

Then, the list of coordinates for each feature is associated with the feature’s tag.

The objects you see in a vector theme are actually saved in the

theme table

Raster data model

• Location is the main focus of representing geographic features.

• Earth is treated as one continuous surface.

• Each location is represented as a cell.• Cells are organized into a matrix or rows

and columns called a grid.

• Each row contains a group of cells with values representing a geographic phenomenon.

• Cell values are numbers, which represent nominal data such as land-use classes or elevation.

• Cells are identified by their position in the grid. Notice that in a grid, cells have eight (8) neighbors (except those on the outside edges); four at the corners and four at the sides.

• Like the vector data model, the raster data model can represent discrete point, line and area features.

• A point feature is represented as a value in a single cell, a linear feature as a series of connected cells that portray length, and an area feature as a group of connected cells portraying shape.

• Because the raster data model is a regular grid, spatial relationships are implicit. Therefore, explicitly storing spatial relationships is not required as it is for the vector data model.

Main component of spatial analyst is the grid theme

(raster data model)

6. What is a grid theme?

• A grid divides geographic space into uniform blocks called cells.

• Used to represent terrain elevation or other phenomena that change gradually across a surface.

Elevation grid looks smooth, but, as the zoomed-in graphic at the bottom indicates, it's really composed of thousands of small cells. Each cell, stores an elevation value for the space it covers (about 16,000 square feet per cell for this grid.)

Two types of grids: • Integer grids store cell values as integers • Floating-point grids store values with

decimal points

7. What is a Surface?

• Grid themes represent a continuous surface• Continuous data, such as elevation or air

temperature over an area. • Surfaces can be represented by models built

from regularly or irregularly spaced sample points on the surface (Interpolation).

• The top graphic below shows a set of sample elevation points used to generate a surface model.

• The bottom graphic shows a spatial model actually created from the points.

8. Using Spatial Analyst Extension

Creates, queries, maps and analyzes data that form continuous geographic surfaces.

Elevation Air temperature Precipitation Chemical concentrations

(pollutants)

Map Algebra• Uses math-like expressions that return

numeric values to an output grid.• Expressions are entered into the Map

Calculator in the Avenue syntax.

Querying Grids

• Select areas spatially by defining a Boolean query based on the values of one or more grid themes.

• Output will be a grid theme with areas that

match the query given a value of 1 (TRUE) and areas that do not match the query given a value of 0 (FALSE).

Classification• Ordering a theme's data values into a

specified number of groups according to a particular method.

• The values in the classified theme are not changed in any way.

• Floating point grid theme - default classification method is Equal Interval, can be changed to Standard Deviation.

• Integer grid theme - can be classified by any of the five methods available: Equal Area, Equal Interval, Natural Breaks, Quantile, or Standard Deviation.

Contours and Surfaces• Can create isolines (a line theme) or a

continuous surface (a grid theme) using a point theme of sampled points.

• Both help analyze continuous change of an attribute over space (elevation, temperature, soils pH level).

Cost surface

• Grid defining the impedance, friction, or cost to move through a cell.

• Used to determine the least cost path between a source and destination (travel time, dollars, fuel).

Proximity Analysis• Analyze the distance between features, find

the closest feature in another theme • Create discreet distance buffers to find

features within a distance of other features.

• A buffer is a zone of specified distance around a feature.

Overlay Analysis

• Compare two or more themes (layers) to reveal new relationships between features in the different themes.

• New grid theme that contains only the features that meet the requirements of your query.

• Map Query - ( [ Landuse . desc] = "Agr" ) and ( [Flood Zone] = 1 )

Visualization

• Visualization techniques are used to create topographic and thematic maps, statistical graphs and to visually render surfaces.

• Hillshading - visualization tool to display hills and valleys in relief. Calculates the effects of illumination on a surface

• Histograms - another important visualization tool available. A histogram is a chart of the distribution of cell values in a grid theme. Useful to see if the values are skewed to one side of the mean or normally distributed.

9. Extending - Spatial Analyst Chapters

1. Start ArcView2. Choose spatial analyst extension (file -

extensions)3. Notice how ArcView interface changes

2 new menus (Analysis and Surface)Histogram buttonContour tool

4. Navigate to extending ArcView datasets (c:\extend) to begin exercises

5. Answer questions for Chapters 8 - 14

Spatial Analysis

• In order to solve any problem by Geographic

information System (GIS) modeling a series

of steps must be followed

• These steps are typical for addressing any

problem with some difference in details for

each problem domain

Spatial Analysis

• Single layer operations (proximity)

• Multiple layer operations (Union, Intersect)

• Network analysis (shortest path)

• Surface analysis (TIN, Aspect, Slope)

• Grid analysis (flow direction, diffusion)

Steps for Spatial Analysis

• Establish analysis objectives and criteria

• Prepare data for spatial analysis (spatial + attribute)

• Perform spatial operations (buffering, overlay, feature extraction)

• Perform tabular analysis using arithmetic and logical operations;

Reselect

Buffer

Intersect

Erase

Flow chart for database

Geographic databaseGeographic database ArcViewshape files

Spatial analysis A system

Transform to real-world co-ordinates

Import to ARC/INFO

Create topology Build and Clean

Check feature accuracy

DigitisationAutoCAD

AttributedBASEIV.

• Evaluate and interpret the results (validity and checking by producing plots and reports)

• Refine the analysis by identifying the shortcomings and limitations of theanalysis

• Produce final maps and tabular report of the results.

Steps for Spatial Analysis- Continue

Example for spatial analysis

Finding suitable dumping site

How can I find a suitable

dumping site, that is

economically,

legally, and

environmentally

sounded?

Find a suitable dumpsite using GIS

• Groundwater contamination

• Surface water contamination

• Soil contamination

• Water and air quality

• Noise pollution

• Human health due to methane and carbon

• Marine environment

Factors to be considered

Economy

Atmosphere

Surface water

Biotic lifeSoilWater

Legality

Dumping site

Environment

Groundwater

Data collection

• Geology, Groundwater

• Rivers, Coastal line

• Soil, Landuse

• Airport, Roads

• Settlements, Hotels

Spatial + Attribute data

Add attribute data

Digitization underAutoCad

Transform to realcoordinate

Import to ARC/INFO

Create topology Build and Clean

Check featureaccuracy

Geographic database ArcView-shape files

Geographic analysis

Steps for data preparation

Feature extraction from a GIS database

• Feature extraction from a GIS database can be done using commands such as CLIP, ERASE, IDENTITY, and RESELECT.

• Logic such as SELECT, ASELECT, NSELECT and boolean operators (= , < >, >, <, >=, <=, EQ, NE, GT, LT,GE, LE, CN, IN).

• These commands can be used to identify areas that met the desired criteria.

Perform spatial operations

• Feature extraction from a GIS database

(Reselect)

• Map overlay (Intersect, Union, Mapjoin)

• Proximity searches (Buffering)

Geographical objects

LanduseTopography

Soil type Utility

RiversRoads

DistrictLots

Example Project Steps

Layer 1: Lake

Layer 2: Forest

Layer 3:Soil Drainage

Layer 4:Loggable Species

Layer 8:Species And Soils

Spread Recode Recode

Layer 5:Drained Soils

Layer 6:Near Lake

Layer 7:Away From Lake

OverLay

Layer 9:Loggable Sites

Recode Recode

Produce final maps and tabular report of the results

System design

User interaction

Reselect

GeologyLand useSoilRainfall

Buffer

RoadsRivers

Intersectsuitable zonesfor each factor

Suitable zones

The best zones

User interaction

Select suitable layer for dumping:

Geology Rainfall Productivity Land use B1 2420 2500 Getah C2 2440 4000 Kelapa C3 2460 6000 Padi D3 2480 Pekan D4

Final zones

Help

Data about geology

Screening

Example for groundwater selection

Confirmation of the selection

Suitable groundwater zones

Unsuitable zones around rivers

Spatial Modelling

Step 1: State your research question(s). Then create a flowchart to organize the data and analyses that you will perform to explore/answer your research question(s) (I will give you an example flowchart).

The following is an example of a research project with a sample flow

chart Your city is looking into alternative energy

sources that will provide clean and inexpensive power for residents. The city has decided to look into solar power since coal pollutes, oil may run short, nuclear is hazardous.

Your data set consists of elevation points and power lines.

You need to generate a list of criteria in aiding you in this siting problem.

To do so you use this diagram:

The list of criteria you develop define your spatial model.

Some spatial analysis problems can be very complex, involving many data sets and processing tasks.

It is often helpful to create a flowchart of the analysis to organize the data and tasks.

The flow chart outlines the solar energy station siting model that would be performed in this

research project: