1 Spatial Analysis [2]

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Spatial Analysis [2]

Dr. Ragab Khalil

Department of Landscape Architecture Faculty of Environmental Design King AbdulAziz University Room 103

LA561 Computer Applications in LA LA561 Computer Applications in LA

(GIS)(GIS)

Dr. Ragab Khalil KAAU - FED – LA561: GIS 2/47

Overview Overview

• Topological Overlay

• Topological Overlay Types

• Buffering

• Model Builder

Topological Overlay 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

•

Topological overlay is different from the Select By Location operations described in the last lesson.

•

In the Select By Locationoperations,

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.

Topological Overlay 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.

Topological overlay:

Topological overlay:

Overview 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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Topological overlay:

Arc/node Arc/node topology data model topology data model

•

Complex spatial data structure

1 2

ð ð

2

3 1

1 3

4 5

#

2

#

3

4

5 6 8 7 ð4

5

3 ð

Topological overlay:

Overview Overview

•

Always uses polygon as the overlay layer

•

Output is the same as the input

Topological overlay

Topological overlay

: How it works : How it works

•

Features come from separate layers

•

No explicit spatial relationship between Streams & Stands

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Topological overlay:

How it works How it works

•

New nodes are created

•

Topology is rebuilt

•

Spatial relationship is made explicit

Topological overlay:

How it works How it works

•

Lines are split at polygon boundaries

•

Lines take on attributes of overlapping polygons

Topological overlay:

How it works How it works

•

Lines are split at polygon boundaries

•

Lines take on attributes of overlapping polygons

Alfisol

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ArcToolbox Extension 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

Overview Overview

•

Topological Overlay

•

Topological Overlay Types

•

Buffering

•

Model Builder

Topological overlay: Types Topological overlay: Types

• Dissolve

• Union

• Clip

• Identity

• Intersect

• Update

• Erase

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Topological overlay:

Dissolve Dissolve

•

Removes boundaries between polygons or nodes between arcs

•

Features with same attributes are dissolved

Topological overlay:

Dissolve Dissolve

Topological overlay: Union 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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•

Start with two polygon layers

•

Geometry of both inputs is retained

•

Tabular structure is maintained

•

ArcToolbox

interface

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Topological overlay:

Identity 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

Topological overlay:

Identity Identity

•

ArcToolbox interface

Topological overlay:

Identity Identity

•

Identity creates new layer and table

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Topological overlay:

Intersect 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

Topological overlay:

Intersect Intersect

•

Topological overlay:

Intersect Intersect

•

New layer is created

•

Both input attributes remain in output

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Topological overlay:

Intersect Intersect

•

Because geometry fields are not automatically updated when shapefiles are overlain, must use other methods of calculating/updating geometry values

Topological overlay:

Update Update

•

All features exist in output

•

“Underlapping” features from input are erased

•

Attributes only from input layer exist in output

•

Order of input and overlay matters

•

Polygon on polygon only

Topological overlay:

Update Update

•

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Topological overlay:

Update Update

• Feature geometry is updated

• Only input attributes are retained

Topological overlay: Clip Topological overlay: Clip

•

“Cookie cutter”

•

Only input layer features and attributes exist in output

•

Polygon on polygon, line, or point

•

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•

Geometries are maintained within the outline of the clipper

Topological overlay: Erase Topological overlay: Erase

• “Cookie cutter”

• Only input layer features and attributes exist in output

• Order of input and overlay matters

• Polygon on polygon, line, or point

Topological overlay: Erase Topological overlay: Erase

• ArcToolbox interface

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Topological overlay: Erase Topological overlay: Erase

•Removes area of overlap

•Only input attributes are retained

Overview Overview

•

Topological Overlay

•

Buffering

•

Model Builder

Buffering Buffering

•

Distance or proximity analysis

•

Constant or variable width from input features

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Buffering Buffering

•

Buffering Buffering

•

Can create a new feature class or coverage

Overview Overview

•

Topological Overlay

•

Buffering

•

Model Builder

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Model Builder 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)

•

Available within ArcToolbox

•

Graphical interface to process modeling in GIS

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•

Tools

•

Data outputs

•

Data inputs

•

Model results can be added to data frame