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Geographic Information Systems (GIS)in Environmental Studies ENVS 3520 3.0 – Lecture 7

Daniella Molnar for - John Sorrell

SeconSys Inc. York Universityjohn.sorrell@seconsys.com sorrell@yorku.ca

Session PurposeSession Purpose::

To discuss vector-based GIS processing, analysis and statistical generalization for mapping thematic distributions.

GIS in Environmental Studies

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Characteristics of Characteristics of the Raster Data the Raster Data Model:Model:

GIS in Environmental Studies

Raster layers

Raster map

Vector map

Actual terrain

forest

drainage

highway

relief

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The Vector Data Model The Vector Data Model ––Spatial Representations:Spatial Representations:

GIS in Environmental Studies

Vector Layers

Vector map

Actual terrain

forest

drainage area

drainage lines

drainage point

highway layer

The Vector Data Model The Vector Data Model ––Attribute Association:Attribute Association:

GIS in Environmental Studies

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Intelligent Structure: Intelligent Structure: (Arc(Arc--Node Topological data Node Topological data model)model)

Topology: a branch of math that defines spatial relationships between features and their properties in elastic space.

GIS in Environmental Studies

Common Topological ErrorsCommon Topological Errors

GIS in Environmental Studies

Floating nodes Odd polygons

Dangling Arcs Sliver polygons

Floating Arcs Polygons missing labels

Overlapping Arc Overlapping polygons

Pg. 93 and 195 in Lo and Yeung

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Topological Topological Relationships:Relationships:

GIS in Environmental Studies

1) Connectivity: Topology keeps track of all connected features - and can be used to derive geometric measurements like length and area.2) Containment : Closed chains of arcs define a polygon and can indicate what is within a polygon 3) Contiguity: Arcs have direction (N2N) and left and right sides. Topology links adjacent feature.

The most important aspects of topology is its capability to recognize surrounding features. The three most important properties that come with topology are the following:

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Topological Data Processing Topological Data Processing Functions with the Vector Functions with the Vector Data Model:Data Model:

Input functions – prepare and structure vector data (data entry, resampling/editing and compilation).

Analysis functions – explore spatial relationship implicit in the source layers using non-topological, feature-based and layer-based functions. (database query, geometric, reclassification, and overlays operations).

Output functions – publishes output to inform decision making (graphs, stats reports and maps).

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NonNon--Topological Functions:Topological Functions:GeoDatabaseGeoDatabase FunctionsFunctions

GIS in Environmental Studies

1) Attribute Database Query2) Statistical Computation3) Address Geocoding4) Computation of Area, Perimeter and Distance

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FeatureFeature--based Topological Functions :based Topological Functions :BufferingBuffering

GIS in Environmental Studies

Original spatial feature

Buffer zones are generated by eachline segment and node of the spatialfeature.

Boundaries of individual elementbuffer a re dissolved to form onecoherent buffer zone.

Used to delineate a specified zone around a vector feature.

LayerLayer--based Topological based Topological Functions:Functions:

ReclassificationReclassification

GIS in Environmental Studies

(a) Original soil map

(d) Land suitability map with boundaries dissolved

(b) Reclassification criteria

(c) Land suitability map

Used to reduce, simplify or reconfigure attribute values to a new measurement scale.

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GIS in Environmental Studies

LayerLayer--based Topological based Topological Functions:Functions:

OverlayOverlay

Two feature layers are combined to create anew derived output layer with new attributecombinations, graphic representations and topology.

Easiest to understand in the context of :

1) The types of overlay2) Topological overlay operators3) Topological overlay process

GIS in Environmental Studies

The Topological Overlay ProcessUNION Operator

M

N

LayerLayer--based Topological based Topological Functions:Functions:

OverlayOverlay -- UNIONUNION

Overheads ->

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Output Functions:Output Functions:How to present the analysisHow to present the analysis

GIS in Environmental Studies

•Graph

•Statistical reports

•And of course, MAP!