introduction to gis - colorado state university...introduction to gis geographic information systems...

9/24/2015

R. Khosla Fall Semester 2015 1

Introduction to GISGeographic Information

Systems

SOCR-377

Geographic InformationSystems

SOCR-377

What in the world is GIS?

GIS is simultaneously thetelescope, the microscope,the computer and the Xeroxmachine of regional analysisand synthesis of spatial data.

(Ron Abler, 1988)

GIS…

Item on the internet’s

comp.infosystems.gis FAQ list (FAQ = frequently asked questions)

GIS…

GIS: An introduction

The real world

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GIS Tools

• GIS is intended to be the means of improving everyday life

• It is important that information generated from data processingbe applied to guide the real world in the right direction

GIS…

Abstraction or

simplification

DataAnalysisResults

High

Medium

Low

50 lbs/ac

Take action

100 lbs/ac150 lbs/ac

Yield maps

The real world

•A traditional map can be both a presentationmedium and a storage medium

GIS…

STORAGE

+PRESENTATION

Traditional Maps

• wide variety of products can be created fromthe same basic data

GIS…

STORAGE

PRESENTATIONEnviron-mental

Roads Utilities Areas Farms

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GIS…Example of data set from Larimer County

Want to look at Cities and Towns in Larimer County

GIS…

40,665600 -104,996072 5347 12.1 Livestock

40,665595 -104,996072 5462 48.6 Cereals

40,665595 -104,996072 5311 7.6 Livestock

40,664756 -104,996646 5426 87.3 Cereals

40,664756 -104,998697 5401 0.3 Buildings

• For presentation purposes, the data in the table is translated into map symbols (objects)

• These symbols are then superimposed on existing map data

Lat Lon Alt Area Category

Table Information

Base map

Map symbol

Maps: http://las.depaul.edu/geography/Programs/CertificateInGIS/index.asp

GIS…

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• By use of GIS a simplified world can be brought into the computer

• Different techniques can be applied to analyze and simplify the data, and foundation is laid for the decision making pyramid

• Today, GIS are in the process of filling the upper half of pyramid

Analysis and refining of data

Decision makingStrategic Level

GIS…

Real world

GIS Chain

• A GIS system cannot be bought off the shelf

• The system has to be built up within an organization.

• When planning to introduce GIS, it is important that equal attention be given to all four links in the GIS chain.

Farmer/Consultant/Agronomist

Farm OperationsWeather

Marketing/OutputPurchases

By yearBy fieldBy Farm

By Operation

MapInfoArcInfo

FarmGPSFarm HMS

GIS…

ExpertiseStructured

dataOrganization

Hardware / Software

One can visualize the data stored as theme layers in the computer, with each layer linked to a common georeferencing system

GIS… Customers

Streets

Parcels

Elevation

Land usage

Real world

Lat: 40.52o

Lon: -105.24o

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Real World Model

Entity:

- Type

- Attributes

- Relationship

• To bring real world into GIS, one has to make use of simplified models of real world

Real World

GIS…

Farm, Forest, City

Crop Farm, Dairy Farm, Livestock Farm, Poultry Farm

Large, Small, Corn, Wheat, Soybean

Land, Equipment, Labor, water, aquifer, ditch

Real World Model

Entity:

- Type

- Attributes

- Relationship

Data Model

Object:- Type- Attributes- Relationship- Geometry: point, line, area

- Quality: quality parameters

Database

Object:- Type- Attributes- Relationship- Geometry- Quality

Real World Maps/Reports

Symbol, Line, Text

GIS…

• To bring real world into GIS, one has to make use of simplified models of real world

• Uniform phenomena can be classified and described in the real world model

• Real world model is converted into data model by applying elements of geometry and quality

• The data model is transferred to a data base (tables/spreadsheets) that can handle digital data

• From which data can be presented/displayed

Real World Real World Model

Buildings

Probable categories

Situated at

Represented by

Height

Governmental40.749668; -73.969170

Polygon

505 ft

Roads

Probable categories

Location

Represented by

Length

Avenue

A. 40.802198; -73.931245

B. 40.7222799; -73.988603

Polyline

125 blocs

ID Type Area X Y Height

1

2

3

Governmental

Commercial

Governmental

0.27

0.02

0.12

40.74

40.75

40.74

-73.96

-73.94

-73.91

505

370

478

Modeling process: The transformation of real world into GIS products is achieved by means of simplification and models in the form of maps and reports.

Final Product: Map Display

GIS…Data model

Database

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Vector dataIn vector data model, the objects are defined as points, lines or polygons.

GIS…

Point

Tree

Line Polygon

LakeFea

ture

sR

eal w

orld

•Examples of a Point feature (Tree)

•A line feature (River) •A polygon feature (Lake)

Vector data…

• Geographic information has dimension

• Areas are 2-dimensional (2D) which consists of lines, which are 1-dimensional, and consists of points, which are zero-dimensional and consist of a coordinate pair

• Entire world of vector data consist of POINTS, LINES AND POLYGONS

GIS…

Longitude Latitude

-105.082771 40.572993

-105.082778 40.572989

-105.082778 40.572981

-105.082763 40.572978

-105.082761 40.572976

-105.082754 40.572970

-105.082748 40.572966

-105.082739 40.572977

Area consist of… Lines, which consist of…

Points, which consist of…

Coordinates

Geometric Objects.

Point: A zero dimensional object that specifies geometric location specified through a set of coordinates.

Line Segment: A one directional segment that is a direct line between two end points.

Link: A one directional object that is a direct connection between two nodes.

Directed Link: A link between two nodes with one direction specified.

String: A sequence of line segments.

Node: A zero dimensional object that is a topological function and may specify a geometric location.

GIS…

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Chain: A directed sequence of nonintersecting line segments with nodes at each end.

Arc: A locus of points that forms a curve that is defined by mathematical function. Also defined as a string or a chain.

Geometric Objects.

GIS…

GIS…

X (Longitude)

Y(L

atit

ude)

Y = mX+bY = 0.23X3 + 0.71X2 – 4.9X – 11.3

ID Longitude Latitude

1 -105.08277 40.572992 -105.08278 40.572993 -105.08278 40.572984 -105.08276 40.572985 -105.08276 40.572986 -105.08275 40.572977 -105.08275 40.572978 -105.08274 40.572989 -105.08277 40.5729910 -105.08278 40.5729911 -105.08278 40.5729812 -105.08276 40.5729813 -105.08276 40.5729814 -105.08275 40.57297

ID Longitude Latitude

1 -105.08277 40.5729914 -105.08278 40.57299

• Each object is assigned attributes and coordinates

• The number of coordinates for lines and polygons will vary considerably, depending on the length of the line and the circumference of the polygon

• This may make it inappropriate to store attributes and geometry together and is one of the reasons that many systems store them separately

Geometry ID Thematic Codes Attributes Coordinates

Point

Line

Area

1

10

100

1000

7000

5000

A B

C D

C E

4, 3 (Single Point)2,1 11, 5…5, 9 (String)14, 10 12, 14…….14, 10 (Closed Polygon)

GIS…

Y

X

1

10100

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• Spaghetti data is a term often used to describe digital map data with crossing lines, loose ends, double digitalization of common boundaries between adjacent polygons and so on.

• These data lie in a pile, just like Spaghetti.

• Several line segments are to be found in odd places in the data file.

MapTable

Line No. Coordinates

1

2

3

.

.

11

.

.

20

X, Y, Z

X, Y, Z

X, Y, Z

1

Y

X

3

20

GIS…Spaghetti data 20 nodes

Raster Data

• A two dimensional object (not bounded by lines)

• It is a method of storing, representing ordisplaying spatial data in digital form

• It consists of cell data (not necessarily square)

• arranged in a regular grid pattern

• in which each unit (pixel or cell) within the gridis assigned an identifying value based on itscharacteristics

GIS…

GridCell

Generic Structure for a Grid

Raster Data

Raster Cell/Pixel: A two dimensional object (not bounded area). It is a method of storing,representing or displaying spatial data in digital form. It consists of cell data (not necessarily square)arranged in a regular grid pattern in which each unit (pixel or cell) within the grid is assigned anidentifying value based on its characteristics

Columns

Row

s

GIS…

Grid Extent

Grid Resolution

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• Raster data can be visualized as a grid lying over the terrain

• Each grid cell has a code stored in the database describing the terrain within the particular cell

GIS…

Coded grid cells1. Buildings2. Trees3. Water bodies

• In raster format, data is stored in cells

• Each cell in a layer has a single attribute

GIS…

Soil layer in vector format

Soil layer in raster format

H

ML

GIS…

VectorRaster

Low resRaster

High res

• The higher the resolution, the smoother the edges

• The higher the resolution the larger the file

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• Only one attribute value may be assigned to each cell

• Objects that have several attributes are therefore represented with a number of raster layers, one for each attribute

GIS…

Forest type

Timber quality

Tree age

• A line and the column number define the cell’s position in the raster data

• The raster data are then stored in the table giving the number and attribute value of each cell

Cell No. Cell Type

11

12

13

14

15

16

17

.

.

76

77

78

.

.

81

82

0

0

1

0

0

2

0

.

.

3

3

0

.

.

2

2

Coded grid cells0. Unmapped1. Buildings2. Trees3. Water bodies

GIS…

GIS…

Point

Tree

Line

Polygon

Lake

Vector dataReal world Raster data

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GIS…

Some data benefit from being in raster format while other benefit from being in vector format

In a raster, every pixel contains information that needs to be stored

In a vector, only components of points, lines and polygons are stored

Converting raster to vector may result in loss of data

GIS…

• A GIS can display and analyze data as

multiple layers of the same field

• Each layer may represent one of the

following: field boundaries, soil pH,

drainage tiles, yield values, etc.

• We could run queries and data analysis

to make a better on-farm decision

GIS…

You are talking to a computer!

Where is the best part of my field?

• Select points where pH is above 8.5 and yieldis below 130 bu/A in field 31

GIS query

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GIS…

GIS query

“DryYield” < 130

GIS…

GIS query

GIS, is a tool which integrates spatial and non-spatial information over time

So, what is GIS?

to make better decisions.

GIS…

introduction to gis - colorado state university...introduction to gis geographic information systems...

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