Geographic Information Systems (GIS) in Environmental · PDF file1 Geographic Information...
Transcript of Geographic Information Systems (GIS) in Environmental · PDF file1 Geographic Information...
1
Geographic Information Systems (GIS)in Environmental Studies ENVS 3520 3.0 – Lecture 7
Daniella Molnar for - John Sorrell
SeconSys Inc. York [email protected] [email protected]
Session PurposeSession Purpose::
To discuss vector-based GIS processing, analysis and statistical generalization for mapping thematic distributions.
GIS in Environmental Studies
2
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
3
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
4
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
5
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:
6
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).
GIS in Environmental Studies
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
7
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.
8
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 ->
9
Output Functions:Output Functions:How to present the analysisHow to present the analysis
GIS in Environmental Studies
•Graph
•Statistical reports
•And of course, MAP!