LA561 Computer Applications in LA (GIS)

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Spatial Analysis

Dr. Ragab Khalil

Department of Landscape Architecture Faculty of Environmental Design

King AbdulAziz University Room 103

LA561 Computer Applications in LA (GIS)

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Where have we come so far?

 By now, you should be familiar with:

• What GIS is

• How GIS works

• Some of what GIS can do

• GIS data formats

• Spatial data

• Tabular data

• Modifying views of data

• Basic operations on data entry and editing

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What comes next?

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Basic vector analysis

 One of the most basic analytical tasks in a GIS is locating features in one layer based on the location of other features in the same layer or in another layer.

 Examples :

• Which city lie within 10 km of a river?

• Which sampling plots have been covered by a recent slope failure?

• Does any road pass through the oldest stands in a forested area?

…

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Basic vector analysis

 Examples:

• What is the age of buildings adjacent to buildings younger than 10 years?

• What is the mean slope of the group of

stands within 50 m of a stream?

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Basic vector analysis Overview

 Analyzing spatial relationships

• Select by location (Layer-on-Layer selection)

• Spatial join

 Topological Overlay

 Topological Overlay Types

 Buffering

 Model Builder

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Analyzing spatial relationships

 Relationships between features

• Proximity

• Containment

• Overlap

 All based on feature geometry

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Select by location

 Layer-on-layer selection

• Selecting points near a line (proximity)

• Selecting adjacent features (proximity)

• Line-on-polygon selection (containment)

• Polygon-on-line selection (overlap)

• Point-in-polygon selection (containment)

• Polygon-on-point selection (overlap)

• Polygon-on-polygon selection (overlap)

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Layer-on-layer selection

 Definitions

• Target layer(s):

the layer(s) we want to know something about

• Selector layer:

the layer we are spatially referencing to

 For a series of streams, find the distance

to the nearest forest stand

target layer

selector layer

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Layer-on-layer selection

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Selecting points near a line (proximity)

 Find inventory plots near streams target layer

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Layer-on-layer selection : feature type relationships

 Spatial relationships follow geometric rules

spatial

relationship purpose target layer

feature types

selector layer feature types are completely within

selects target layer features that are completely within selector layer features

point line polygon

polygon

completely contain

selects target layer features that completely contain selector layer features

polygon

point line polygon have their center in

selects target layer features whose centers fall inside selector layer features

point line polygon

polygon

contain the center of

selects target layer features which contain the centers of selector layer features

polygon

point line polygon intersect

selects target layer features that intersect

selector layer features

point line polygon

line polygon

are within distance of

selects target layer features that are within a given distance of selector layer features

point line polygon

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Spatial join

 Spatial join

• Spatial join: containment

• Spatial join: proximity

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Spatial join

 Layers are joined based on geometry

• Features are related and compared for distance and containment

• Based on feature geometry

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Spatial join

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Spatial join

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Spatial join: containment

 Records are joined for features within other features

 polygon attributes are

attached to points

 related fields can be

used for display

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Spatial join: proximity

 Appends tables and automatically adds

distance field distance from each plot center point to the closest road line

distance used as

display field

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Overview

 Buffering

 Model Builder

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological Overlay

 Topological overlay allows us to ask questions like:

• "Where are locations that are on stable soils,

• with a slope in the range of 5-10%,

• that were within 15 km from the main road,

• on low productivity sites, and

• what is their percentage of area with respect

to the entire zone?"

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Topological Overlay

 Topological overlay is different from the Select By Location operations described earlier.

 In the Select By Location operations,

• ArcGIS only looks at the spatial overlap of the features of two layers, and

• Creates a new selected set in one of those layers;

• No new data sets are produced; no attribute

updates are made.

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological Overlay

 In Topological overlay,

• new layers are created whose geometry and/or attribute structure are altered.

• allows us to find overlapping features, as

well as to quantify the area or length of

overlap.

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Topological overlay: Overview

 Uses arc-node topology data model for layer- to-layer relationships

 Relationships of containment

 Various analytical functions

 Quantify length/area of overlap

 All functions are accessed with ArcToolbox

tools

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Overview

 Always uses polygon as the overlay layer

 Output is the same as the input

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Topological overlay : How it works

 Features come from separate layers

 No explicit spatial relationship between

Streams & Stands

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: How it works

 New nodes are created

 Topology is rebuilt

 Spatial relationship is made explicit

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Topological overlay: How it works

 Lines are split at polygon boundaries

 Lines take on attributes of overlapping

polygons

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: How it works

 Lines are split at polygon boundaries

 Lines take on attributes of overlapping polygons

Alfisol

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ArcToolbox Extension

 ArcGIS module for geoprocessing

 Part of “core” ArcGIS

 Contains controls for several different

topological overlay types

 Does NOT

automatically update

geometry fields for

shapefiles

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Overview

 Buffering

 Model Builder

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Topological overlay: Types

 Dissolve

 Union

 Clip

 Identity

 Intersect

 Update

 Erase

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Dissolve

 Removes boundaries between polygons or nodes between arcs

 Features with same attributes are dissolved

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Topological overlay: Dissolve

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Union

 All input features from both layers remain

 Attribute values are assigned by containment

 Attribute inheritance

 Polygon & polygon only null value = ""

null

value = 0

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Topological overlay: Union

 Start with two polygon layers

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Union

 Geometry of both inputs is retained

 Tabular structure

is maintained

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Topological overlay: Union

 ArcToolbox interface

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Identity

 All features from input layer persist

 Attributes from both layers exist where there is overlap

 Order of input and overlay matters

• polygon on polygon, line, or point

1

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Topological overlay: Identity

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Identity

 Identity creates new layer and table

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Topological overlay: Intersect

 Only features from overlap area exist in output

 Attributes from both layers exist

 Order of input and overlay does not matter

 Polygon on polygon, line, or point

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Intersect

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Topological overlay: Intersect

 New layer is created

 Both input attributes remain in output

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Intersect

 Because geometry fields are not automatically

updated when shapefiles are overlain, must

use other methods of calculating/updating

geometry values

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Topological overlay: Update

 All features exist in output

 “Underlapping” features from input are erased

 Attributes only from input layer exist in output

 Polygon on polygon only

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Update

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Topological overlay: Update

 Feature geometry is updated

 Only input attributes are retained

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Clip

 “Cookie cutter”

 Only input layer features and attributes exist in output

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Topological overlay: Clip

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Clip

 Geometries are maintained within the outline

of the clipper

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Topological overlay: Erase

 “Cookie cutter”

 Only input layer features and attributes exist in output

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Topological overlay: Erase

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Topological overlay: Erase

 Removes area of overlap

 Only input attributes are retained

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Overview

 Buffering

 Model Builder

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Buffering

 Distance or proximity analysis

 Constant or variable width from input features

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Buffering

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Buffering

 Can create a new feature class or coverage

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Overview

 Buffering

 Model Builder

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Model Builder

 Graphical interface to process modeling in GIS

 “Self documenting”/Exposed

 File-based, stored with map document, or stored with geodatabase

 Can be shared

 Built-ins, VBA, scripted tools (perl, Python,

Java, etc)

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Model Builder

 Available within ArcToolbox

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Model Builder

 Graphical interface to process modeling in

GIS

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Model Builder

• Tools • Data outputs

• Data inputs

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Model Builder

 Model results can be added to data frame

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Dr. Ragab Khalil KAAU - FED – LA561: GIS Dr. Ragab Khalil KAAU - FED – LA561: GIS

Summary

 Select by location

 Spatial join

 Buffering

 Model Builder