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Advanced GIS

Topic 1

Starting Jan. 16, 2007

Outlines

"About the class setting "Materials to be covered and scheduled "Quick review of GIS basics "First lab

Materials to be covered and

scheduled "Review (week 1,2) "Geodatabase lab 1 "Spatial data analysis (3,4,5) "Vector data analysis (lab 2) "Raster data analysis "Basic (lab 3) "Watershed delineation (lab 4) "Geostatistic analysis (6,7,8) "Lab5,6 "3-D analysis (10,11,12) "Lab7,8 "Geoprocessing (13,14,15) "Lab9,10

What is GIS ?

A computer system for

-collecting, -storing, -manipulating, -analyzing, -displaying, and -querying geographically related information.

In general GIS cover 3

components "Computer system "Hardware "Computer, plotter, printer, digitizer "Software and appropriate procedures "Spatially referenced or geographic data "People to carry out various management and analysis tasks

Geographic Data

"Geospatial datatells you where it is and attribute datatells you what it is.

Metadatadescribes

both geospatial and attribute data. In GIS, we call geographic data as GIS data or spatial data

Traditional method

"To represent the geographic data is paper-based maps "Geology map "Topographic map "City street map (we still use it a lot)

Characteristics of spatial data

"³PMSSMNOH´ ŃOMUMŃPHULVPLŃV "Location (coordinate system, will be lectured later) "Size is calculated by the amount (length, area, perimeter) of the data "Shape is defined as shape (point, line, area) of the feature "Discrete or continuous "Spatial relationships

Discrete and continuous

"Discrete data are distinct features that have definite boundaries and identities "A district, houses, towns, agricultural fields,

ULYHUV OLJORM\V "

"Continuous data has no define borders or distinctive values, instead, a transition from one value to another "Temperature, precipitation, elevation, ...

GIS: a simplified view of the real

world "Points "Lines "Areas "Networks "A series of interconnecting lines "Road network "River network "Sewage network "Surfaces "Elevation surface "Temperature surface

Discrete features

Continuous features

Problems caused by the simplified

"Dynamic nature (not static) "Forest grow "River channel change "City expand or decline "Identification of discrete and continuous features "Road to be a line or a area? "Scale "Some may not fit to any type of features: fuzzy boundaries "Transition area between woodland and grassland Lets do not worry about these problems now!!! Just keep in mind

Points

"A point is a 0 dimensional object and has only the property of location (x,y) "Points can be used to Model features such as a well, building, power, pole, sample location ect. "Other name for a point are vertex, node Point Lines "A line is a one-dimensional object that has the property of length "Lines can be used to represent road, streams, faults, dikes, maker beds, boundary, contacts etc. "Lines are also called an edge, link, chain, arc "In an ArcInfo coverage an arc starts with a node, has zero or more vertices, and ends with a nodeLine

Areas (Polygons)

"A polygon is a two-dimensional object with properties of area and perimeter "A polygon can represent a city, geologic formation, dike, lake, river, ect. "Other name for polygons face, zone Area

Topology needed

"A collection of numeric data which clearly describes adjacency, containment (coincidence), and connectivitybetween map features and which can be stored and manipulated by a computer. "A set of rules on how objects relate to each other "Major difference in file formats "Higher level objects have special topology rules

How Topology Works

"We previously discussed that lines represent linear features, or borders for area features. We also said that every line starts and ends with a node, and has intermittent shape points called vertices to define the shape of the line or border. exist. They simply represent a relationship between two nodes and zero or more vertices. "When two lines cross, and form an intersection, they also have a node, since the intersection is the start of one line and the end of the other line. "Topology describes the connectivityof the lines and nodes. So for our example on the right, lines

Aand Bare connected by node b. So line Agoes

from node ato node b. Line Bgoes from node b to node c. "Now, we can create a whole string of lines and put them together into an area too. Now, just like a represent the relationship among lines, which in turn represent the relationship among points. Node Line

Polygon

bABa c

©Arthur J. Lembo

Cornell University

How Topology Works

"Now we have described our location(with x,y coordinates), and our connectivity. What if we had two polygons P1and P2, could we define the adjacency? Yes, here is how: "Line 1goes from node ato node b. "Line 2goes from node ato node b. "Line 3goes from node bto node a. "Polygon P1is to the left of line 2, and to the right of line 1. "Polygon P2is to the right of line 2, and to the right of line 3. "6R RH ŃMQ ŃUHMPH M PMNOH POMP ³ŃOHMUO\ describes location, adjacency, connectivity and containment, or more specifically, a topology table. a bP1 P2 2 1 3

Polygon Lines

P1 1,2

P22,3 Line FromNode ToNode LeftPolygon RightPolygon

1ab0P1

2ab P1 P2

3 b a 0 P2

©Arthur J. Lembo

Cornell University

Traversing Topology

"Without looking at the picture, you can answer these questions from the table: "Where is node a. "No problem. It has an x,y coordinate "What polygon is P1 next to, and where are they adjacent: "P1 is next to P2 because Line 2 has polygon P1 to the left and P2 to the right. This is adjacency. "How do I traverse from node b, to node a, and then back to node b: "Easy! Take line 3to node a, and you have a choice to take either line 2or 3back to node b. This is connectivity. "What lines does polygon P1 fall inside of: "Easy! Polygon P1 is contained by lines 1 and 2. This is containment a bP1 P2 2 1 3 Line FromNode ToNode LeftPolygon RightPolygon

1ab0P1

2ab P1 P2

3 b a 0 P2

Polygon Lines

P1 1,2

P22,3

©Arthur J. Lembo

Cornell University

Topology

© Paul Bolstad, GIS Fundamentals

Two basic data models to

represent these features "Raster spatial data model

"Define space as an array of equally sized cells arranged in rows and columns. Each cell contains an attribute value and location coordinates

"Individual cells as building blocks for creating images of point, line, area, network and surface "Continuous raster

"Numeric values range smoothly from one location to another, for example, DEM, temperature, remote sensing images, etc.

"Discrete raster

"Relative few possible values to repeat themselves in adjacent cells, for example, land use, soil types, etc.

"Vector spatial data model "Use x-, y-coordinates to represent point, line, area, network, surface

"Point as a single coordinate pair, line and polygon as ordered lists of vertices, while attributes are associated with each features

"Usually are discrete features

DIGITAL SPATIAL DATA

RASTER

VECTOR

Real World

Source: Defense Mapping School

National Imagery and Mapping Agency

Raster and Vector Data Models

Vector Representation

X-AXIS

500
400
300
200
100

600500400300200100

Y-AXIS

River House 600
Trees Trees B B BB B B B BG G BK B B B G G GG G

Raster Representation

12345678910

1 2 3 4 5 6 7 8 9 10

Real World

G G

Source: Defense Mapping School

National Imagery and Mapping Agency

Example: Discrete raster

Xie et al. 2005

Example: continuous raster

RasterReal worldVectorHeywood et al. 2006

Effects of changing resolutionHeywood et al. 2006

Vector ±Advantages and

Disadvantages

"Advantages "Good representation of reality "Compact data structure "Topology can be described in a network "Accurate graphics "Disadvantages "Complex data structures "Simulation may be difficult "Some spatial analysis is difficult or impossible to perform

Raster ±Advantages and

Disadvantages

"Advantages "Simple data structure "Easy overlay "Various kinds of spatial analysis "Uniform size and shape "Cheaper technology "Disadvantages "Large amount of data "IHVV ³SUHPP\´ "Projection transformation is difficult "Different scales between layers can be a nightmare "May lose information due to generalization

GIS data formats (files)

"Shapefiles "Coverages "TIN (e.g. elevation can be stored as TIN) "Triangulated Irregular Network "Grid (e.g. elevation can be stored as Grid) "Image (e.g. elevation can be stored as image, all remote sensing images)

Vector data

Raster data

Shape Files

"Nontopological "Advantages no overhead to process topologyquotesdbs_dbs17.pdfusesText_23

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