Introduction to Geographic Information Systems

transcript

Miles Logsdonmlog@u.washington.edu

GIS - consists of:

Components People, organizational setting Procedures, rules, quality control Tools, hardware & software Data, information

Functions Data gathering Data distribution

Geographic Data ( i.e. not spatial information)

Spatial Data location shape relationship among

features

Descriptive Data attributes, or characteristics of

the features

Spatial Data: the spatial attribute is explicitly stated and linked to the thematic attribute for each data item.

Spatial Information

Three Attributes of Geographic Data that constitutes Information Thematic (Value Variable)

Nominal, … name, label Ordinal, … rank ordered Interval / Ratio, … measurement on a scale

Spatial (location) Temporal

After Sinton, 1978:Components of spatial information: time, space, theme (attribute)

Sounds obvious. One must be fixed, one controlled, one measured.

Spatial - thematic value types

Sta. 94, DOC 4.9

WELL200’

100’

200’

Former Land Fill

URBANDuvall, pop 1170

FOREST

AGRICULTURE

Snoqualmie River, 1

BrushCreek, 2

Stream,3

GeographiesLayers, Coverages, Themes

Land useSoils

Streets

Hydrology

Parcels

Concept of Spatial Objects POINTS

Spatial Encoding - RASTER

00 0 0

3311 2

Spatial Encoding - VECTORPOINT - x, y

LINE - x1, y1- x2, y2..- xN, yN

Area (Polygons)

- x1, y1- x2, y2..- xN, yN (closure Point)

* a single node with NO area

* a connection of nodes (vertices) beginning with a “to” and ending with a “from”

(Arcs)

* a series of arc(s) that close around a “label” point

Vector - TopologyObject Spatial Descriptive

x1,y1x2,y2x3,y3

VAR1 VAR2

Fnode Tnode x1y1, x2y21 2 xxyy, xxyy2 3 xxyy,xxyy

10, 11, 12, 1510, …….

Raster Data Model

Set Selections

Reduce Select - RESEL GT 5 = [6 7 8 9 10]

Add Select - ASEL EQ 5 = [5 6 7 8 9 10]

Unselect - UNSEL GE 9 = [5 6 7 8 ]

Null Select - NSEL = [1 2 3 4 9 10 ]

[ 1 2 3 4 5 6 7 8 9 10 ]

AND, OR, XOR

1 2 32

AND = 2

= 1,2,3

Spatial Overlay - UNION

1516 17

# attribute

# IN attribut OUT attribute

102103

102 A A 102 B 102

Spatial Overlay - INTERSECT

# attribute

102103

A 102 B 102 A 103 B 103

Spatial Overlay - IDENTITY

# attribute

102103

A A 102 B 103 B

10 1112 13

Spatial Poximity - BUFFER

Constant Width

Variable Width

Spatial Poximity - NEAR

Assign a point to the nearest arc

Spatial Proximity - Pointdistance

2,0451,8991,743

DISTANCE

Spatial Proximity - Thiessen Polygons

Map AlgebraIn a raster GIS, cartographic modeling is also named Map Algebra.

Mathematical combinations of raster layers several types of functions: • Local functions • Focal functions • Zonal functions • Global functions

Functions can be applied to one or multiple layers

Local FunctionSometimes called layer functions -

Work on every single cell in a raster layer

•Cells are processed without reference to surrounding cells

•Operations can be arithmetic, trigonometric, exponential, logical or logarithmic functions

Local Functions: Example•Multiply by constant value

•Multiply by a grid

2 0 1 1 2 3 0 4 1 1 2

6 0 3 3 6 9 0 12 3 3 6

2 0 2 2 3 3 3 3 2 2 2

4 0 2 2 6 9 0 12 2 2 4

Focal FunctionFocal functions process cell data depending on the values of neighbouring cells

We define a ‘kernel’ to use as the neighbourhood •for example, 2x2, 3x3, 4x4 cells

Types of focal functions might be: •focal sum, •focal mean, •focal max, •focal min, •focal range

Focal Function: Examples

2 0 1 1 2 3 0 4 2 1 1 2

2 3 3 2

2 0 1 1 2 3 0 4 4 2 2 3

1 1 3 2

•Focal Sum (sum all values in a neighborhood)

•Focal Mean (moving average all values in a neighborhood)

1.8 1.3 1.5 1.5 2.2 2.0 1.8 1.8 2.2 2.0 2.2 2.3

2.0 2.2 2.3 2.5

(3x3) 12 13

Zonal FunctionProcess and analyze cells on the basis of ‘zones’

Zones define cells that share a common characteristic Cells in the same zone don’t have to be contiguous

A typical zonal function requites two grids •a zone grid which defines the size, shape and location of each zone •a value grid which is processed

Typical zonal functions •zonal mean, •zonal max, •zonal sum, •zonal variety

Zonal FunctionAn Example

•Zonal maximum – Identify the maximum in each zone

Useful when we have different regions “classified” and wish to treat all grid cells of each type as a single “zone” (ie. Forests, urban, water, etc.)

2 2 1 1 2 3 3 1 3 2

1 1 2 2

1 2 3 4 5 6 7 8 1 2 3 4

5 6 7 8

5 5 8 8 5 7 7 8 7 8

8 8 8 8

Global functionIn global functions -

•The output value of each cell is a function of the entire grid

•Typical global functions are distance measures, flow directions, or weighting measures.

•Useful when we want to work out how cells ‘relate’ to each other

Golbal FunctionAn Example

•Distance Measures – Euclidean distance based upon cell size

Or – some function which must consider all cells before determining the value of any cell – (“cost” associated with a path across the surface)

1 1 1 2

2 1 0 01.4 1 1 0 1 0 1 1

1.4 1 1.4 2

Examples

outgrid = zonalsum(zonegrid, valuegrid)

outgrid = focalsum(ingrid1, rectangle, 3, 3)

outgrid = (ingrid1 div ingrid2) * ingrid3

Spatial ModelingSpatial modeling is analytical procedures applied with a GIS. Spatial modeling uses geographic data to attempt to describe, simulate or predict a real-world problem or system.

There are three categories of spatial modeling functions that can be applied to geographic features within a GIS: •geometric models, such as calculating the Euclidean distance between features, •coincidence models, such as topological overlay; •adjacency models (pathfinding, redistricting, and allocation)

All three model categories support operations on spatial data such as points, lines, polygons, tins, and grids. Functions are organized in a sequence of steps to derive the desired information for analysis.

The following references are excellent introductions to modeling in GIS:Goodchild, Parks, and Stegaert. Environmental Modeling with GIS. Oxford University Press, 1993.Tomlin, Dana C. Geographic Information Systems and Catograhic Modeling. Prentice Hall, 1990.

Introduction to Geographic Information Systems

Documents