21 January Gis

8/7/2019 21 January Gis

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Basics of Geo ra hic InformationSystems

Geographical Technologies for Disaster Risk Management IN84.22, Lal Samarakoon


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What is GIS?

GIS is a set of tools that allow for the processing ofspatial data into information.

This set of tools is open ended, but will include

data input, data storage, data manipulation,p y .

Geo ra hic Information S stem GIS is defined as

an information system that is used toi np u t , st o r e , r e t r ieve , m an ipu la t e , ana lyze and

o u t p u t

geographically referenced data or geospatial,planning and management of land use, naturalresources, environment, transportation, urban


aci ities, ea t services so on.


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Geographic Information Technologies

Global Positioning Systems (GPS)

-

(100 meter to sub-cm) location on the earths surface (in lat/long

coordinates or e uiv

Remote Sensing (RS)

surface

Di ital ortho ima es a ke roduct ma accurate di ital hotos

Geographic Information Systems (GIS)

at a minimum com rises a ca abilit for in ut stora emanipulation and output of geographic information


- an are sources o nput ata or a .

- A GIS a systems for storing and manipulating GPS and RS data.


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How GIS differs from Related Systems

DBMS--typical MIS data base contains implicit but not explicit locationalinformation

, , , .

Automated Mapping (AM) --primarily two-dimensional display devices

thematic ma in unable to relate different eo ra hical la ers (e. zi codes

and counties)

automated cartography--graphical design oriented; limited database ability

ac y anagemen ys ems--

lack spatial analysis tools

CAD/CAM com uter aided desi n/draftin -- rimaril 3-D ra hic creation

(engineering design) & display systems

not referenced via geographic location limited (if any) database ability (especially for non-spatial data)

Scientific Visualization Systems--sophisticated multi-dimensional graphics, but:


lack two-dimensional spatial analysis tools


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Why GIS is unique?

GIS handles Spatialinformation

Information referenced by its location in space

GIS makes connections between activities based on

GIS can integrate data and models to generaten ormat on an scenar os

GIS can penetrate to user group with strongpresentation skills



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Geographic Information Systems

anagemen erspec ve

Decision

Define

roblemDecision

Define

roblem

Output Define GISOutput Define GIS

GIS Import or

build datasetsGIS Import or

build datasets


?


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Problem defining:

Analysis:Management Perspective

What would happen if . . .A chemical leaked into a river?

Where does . . .

Future flood occurrences and population vulnerability?

. . .

Population changed over the last ten years? Where? Is there any changes in river discharge. . .

What is the status o watershed, sediment in u stream?



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Planning & GIS



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Interpretation of Real World in GIS Terms

Villages

Roads

Land Parcels

Land Use

Elevation

Disintegrate


Real World


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Identify location for New

What are the geophysical needs?

How far from present facility locations?

What are the conflicts land uses?

What are the infrastructure needs?

What will be the future?What is the service area?

What will be the size?


Real World space or location related?


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Plan for a New Health facility

Identify location with suitable geo-physical conditions

To o ra h , land use, water, accessibilit , etc.

Identify the serviceable area and the population

Availability of infrastructure

Inquire industries in the vicinity

on c or resources an any rea o opera on

Are there similar operations in the vicinity and conflict

What is the market size

Land prices (Land usage restrictions)


Potential for disasters (floods, typhoon, earthquakes etc.)


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Map: Scale

Ma s are made to scale that is there is a direct connection

between a unit of measurement on the map and the actual

distance. For example, 1: 1 mile map, each inch on the map represents

one mile on Earth. So if you have 2 inches on a map, then it

represent m es n t e rea -wor usually recorded as a ratio, such as 1:100,000, or a fraction,

suc as :

Large scale maps, such as 1:10,000, show finer detail

ma sca e maps, suc as : , , s ow grea er areas



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= ,

50 meter



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,

500 meter



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Ma : Grid and Coordinates

Shows the placement of the parallels and meridians

on maps Used to determine latitude and longitude

determine coordinates only to determine extents



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Latitude and Longitude

The earth is divided into lots of lines called latitude and

longitude.



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Lines

Longitude lines run north and south.

Latitude lines run east and west.

The lines measure distances in degrees.

Latitude

Longitude



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Where is 0 de ree Latitude?

. The equator is 0 degree latitude.

between the North Pole and the South Pole.

Northern HemispheresNorthern Hemispheres



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Where is 0 degree Longitude?

. The prime meridian is 0 degrees longitude. This

imaginary line runs through the Greenwich of UnitedKingdom

Prime Meridian



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Map Legends



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The Earth is divided into 24 time zones, corresponding

to 24 hours in a day. As the earth rotates, the sun shines in different areas,

moving from east to west during the course of a day.

Places that have the same longitude will be in the sametime zone



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GIS components:

Spatialdata

G I SG I S

Specific applications/decision making objectives

ComputerComputer hardware //software toolssoftware tools



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Hardware Environment

Input Output



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Software EnvironmentData Output

Creation of map layouts

Data Input

Enter coordinate information Printing maps

Creating digital maps

Writin data to different

Enter attribute information

Import data from other sourcesformats Detect error in data input

Data Analysis Attribute queries

Spatial interpolation

Network analysis

Terrain analysis

Spatial overlay


eograp c sua za on

Mathematical functions

S f I


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Software Input

Just as GIS required hardware to enter data, software must also be.

modules that allow users to:

Enter coordinate information: software interfaces with adigitizer allow a user to point and click on locations (digitize) tocreate the appropriate representation of geographic objects.

n er a r u e n orma on: so ware n er aces a ow a user

to enter information about a geographic object.

Im ort data from other sources: software interfaces allow auser to import data from GPS units, satellite data, digital photos,scanned maps, or even from other systems.

Detect error in data input: When entering coordinate data intoa GIS, errors will abound. Therefore, GIS software includes



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Software Data Analysis

Data Analysis: GIS software allows us to perform multiple operations ongeographic data. Following is a list of the more popular GIS analysis performedby the software:

Spatial queries: allow us to ask where things are in relation to other things

Attribute queries: allow us to ask questions about the attributes of

Spatial interpolation: allow us to predict some value at a geographic locationthat we have not measured.

Buffer analysis: allow us to analyze the relationship of objects based ondistance

Terrain analysis: allow us to perform three dimensional analysis.

Spatial overlay: allow us to determine the relationship between different

geographic features Geographic Visualization: allow us to visualize geographic data in three

dimensions, or through charts and graphs


, ,functions to geographic features.


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Software Database Management

Database Mana ement: GIS allows us to inte rate

information and geography. This requires software to actually

store and retrieve information. The most common methods forstoring geographic information is in a database. Database

technology allows the software to efficiently store and quickly

.

More advanced database management systems within GIS

,

accessing the data, and provide documentation of the data.



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Finally, GIS software has the ability allow users to prepare

GIS data for output. Some of the functions for data outputinclude:

:

Printing maps:

Writing data to different formats:



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Geographic Information System & Data

Spatial Data Features that have a known location on

.

Attribute Data The information linked to the geographic

Data Layers Result of combining spatial and attribute

data. Essentiall addin the attribute database

to the spatial locationLayer Types Layer type refers to the way spatial and

attribute information are connected. There are

two major layer types, vector and raster.Topology This define how geographic features are

related to one another, and where they are in


relation to one another


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Data types

The data model represents a set of guidelines to convert the real world

consisting of the attributes and geometry.

ere are wo ma or ypes o geome r c a a mo e

a. Vector Model

Vector model uses discrete points, lines and/or areas corresponding todiscrete objects with name or code number of attributes.

b. Raster Model

Raster model uses regularly spaced grid cells in specific sequence. An

e emen o e gr ce s ca e a p xe w c con a ns a s ng e va ue

of attributes.



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Representing Spatial Elements

VECTOR

Real World



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Vector Data Structures

The method of representing geographic features by the

as c grap ca e emen s o po n s, nes an po ygon ssaid to be the vector method, or vector data model

A raster is a tesselation of a surface.

through the repeated use of a single shape.)


d d l


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Raster and Vector Data Models

Real World

500

600

Trees

S

S

G G

G

1 2 3 4 5 6 7 8 9 10

1

2

400

300

Y-AXIS

House

Trees

S

SS G

G

U

S

GG

45

6

200

100River

S

S S

S7

8

9

G

Vector Representation

X-AXIS

Raster Representation


Source: Defense Mapping SchoolNational Imagery and Mapping Agency


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Structure of Vector Data

There is a certain amount of relationship between vector

.

format, data is typically stored as:

Points: points are zero dimensional objects, and

Point

,

locations, or trees.

Lines: lines represent one dimensional objects, or linear

, .

made up of a series of interconnected points. A linetypically starts and end with a special point called a Line

,

called vertices.

Polygons/Area: polygons represent two dimensional

, ,the outline of a building or lake. Polygons are made up

of a series of connected lines where the starting point of Area


.

f


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Structure of Vector Data

Points are zero dimensional objects, which have

be represented as areas.Nodes are special type of point on line features

re resentin a unction or end oint of a line.

Lines are one dimensional objects which have length

. .

Areas or Polygons are closed mathematical figures of

any shape or size. They are formed by a series of

connected lines.


Attribute Data


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Attribute Data

Attribute data are the information linked to the geographicfeatures (spatial data) that describe them. That is, attribute data

are t e non-grap c n ormat on assoc ate w t a po nt, ne,

area, or raster elements in a GIS.

Data Layers


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Data Layers

Data layers are the result of combining spatial and attribute data.Essentially adding the attribute database to the spatial location.

V t D t L


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Vector Data Layers

A layer type refers to the way spatial and attribute information areconnected. Vector data (point, Line, Polygon) data layers are

generate as separate ata ayers. ey cant m x.

Vector: Points, lines and polygons (spatial data) associated withdatabases of attributes (attribute data) are considered vector layer types.

O O 2 1 11

O 0 2

2O

O O

1

2

1

1 1

1

1

11 1 O 11 1

Points Features


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Points Features

Soil Samples

Spill Locations

PH

Type of Spill

Utility Poles

Village

Height

Population

Fire Hydrant



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Lines or Arcs

Street Name Depth

Address Ranges

Water Main

Quality

Flow Rate

Pipe size SS

Date Installed

Lines do not have an area. How to represent

the area of a river or a road?


A P l


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Areas - Polygon Land Use

Land use t e

Area

Soil Boundaries

Type

Flood Zones

Occurrence

Landslide Risk Area


?


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Points are zero dimensional objectsHow to represent area/size of a small dam if represented as a

point eature

Lines do not have an area. How to represent the area of a

river or a road?

Representation of features in Point or Polygon is scale

. .



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a raster based system stores data by using a grid of cells

a un que re erence coor na e represen s eac p xe e er a a corneror in the middle of the cell

each cell or pixel has discrete attributes assigned to it raster data resolution is dependent on the pixel or grid size and may

vary from sub-meter to many kilometres.

, ,

geology, forest type, rainfall rate, etc. generally, raster data requires less processing than vector data, but it

consumes more computer storage space.

remote sensors on satellites store data in raster format

continuous data (FIELD) suit a raster structure


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ESRI, Modeling Our World


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Vector Data Layers


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Vector Data Layers

A layer type refers to the way spatial and attribute information areconnected. There are two major layer types, vector and raster.

Vector: Points, lines and polygons (spatial data) associated with

databases of attributes attribute data are considered vector la ertypes.

O

O

O 2

1

1

1

11O

1

01

2

O O

11 1 21

O 11

1

11

Raster: A row and column matrix (pixels) of X & Y space with

attribute information associated with each pixel is considered a rasterlayer type.O

2O

O 2

1

1

1

1

1

O

10 : WATER


O O

11 1

2 1

O

1

1

1

1

2 : WETLAND

Comparison of Raster and Vector Data Models


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Comparison of Raster and Vector Data Models

Raster Model Vector Model

Advantage: Advantage:

1. It provides a more compact data structure. .

2. Overlay operations arethan the raster model.

2. It provides efficiently encoding of

eas y an e c ent y mp emente .

3.High spatial variability is efficiently

topology and as result more efficiently

implementation of operations that require

represented in raster format.

4.The raster format is more or less

opo og ca n orma on, suc as ne wor

analysis.

required for efficient manipulation

and enhancement of digital images.

.

supporting graphics that closely approximate

Hand-drawn ma s.


Map Projections


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Map Projections

A map projection is any method of representing thesur ace o a s here or other three-dimensional bod

on a plane (Wikipedia)

all map projections are attempts to portray the

surface of the earth on a flat surface

distortions of shape, distance, direction, scale, andarea result from this process

some projections minimize certain distortions while

maximisin others other projections are attempts to moderately distort

.


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,world-wide by dividing the surface of the Earth into 6o

zones, each mapped by the Transverse Mercator projectionwith a central meridian in the center of the zone.

UTM zone numbers designate 6 degree longitudinal stripsexten ng rom egrees out at tu e to egrees

North latitude.

north and south from the equator


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Coordinate Systems


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a coordinate system is a system which uses one or morenumbers, or coordinates, to uniquely determine the position of a

point or other geometric element. The order of the coordinates is

significant and they are sometimes identified by their position in

an or ere s o e emen s an some mes y a e er, as n e x-

coordinate (Wikepedia). There could be many systems such as


Geographic Coordinate Systems


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ne o t e most common

coordinate systems in use is the

,

which uses degrees of latitude and

longitude to describe a location onthe earths surface.

In the northern hemisphere degrees of latitude are measured fromzero at the equator to 90 at the north pole. In the southern

hemisphere it is zero at the equator 90 at the south pole. Lines of

longitude run perpendicular to the equator and converge at the

.


Latitude, Lon itude, Hei ht


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Latitude, Lon itude, Hei ht

the most commonly used coordinate system

the Prime Meridian and the Equator are used to definelatitude and longitude

latitude and longitude are defined as:

degrees, minutes, seconds

360o around the earth

each degree is divided into 60 minutes

each minute is divided into 60 seconds

decimal degrees

a degree expressed as a decimal (in degree units)

Geographic Coordinate Systems


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The Universal Transverse Mercator (UTM) geographic coordinate

system is a grid-based method of specifying locations on the surface

-

Cartesian coordinate system. It differs from the traditional method of

latitude and lon itude in several res ects.

The UTM system is not a single map projection. The system instead

employs a series of sixty zones, each of which is based on a

specifically defined secant transverse Mercator projection.

Each of the 60 longitude zones in the UTM system is based on a transverse Mercator

projection, which is capable of mapping a region of large north-south extent with alow amount of distortion. By using narrow zones of 6 (up to 800 km) in width, and

reducing the scale factor along the central meridian by only 0.0004 to 0.9996 (a

reduction of 1:2500), the amount of distortion is held below 1 part in 1,000 inside

each one. Distortion o scale increases to 1.0010 at the outer one boundaries alon


the equator (Wikepedia).

Data acquisition


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As data acquisition or data input of geospatial data in digital format ismost expensive and procedures are time consuming. In GIS, the datasources for data ac uisition should be carefull selected considerinthe application and scale.

The following data sources are widely used:Analog maps

Elevation, soil, landuse, climate, etc.

Aerial photographs

DEM, landuse (Urban)

ate te mage

Landuse (regional), vegetation, temperature, DEM

Detailed information


Attributes, statistics

Choice of data acquisition method


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Vector data input (map digitizing)


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ep : a x a map o a g z ng a e

Step 2 : add control points or tics at four corners and inputcoordinates

Step 3 : digitize map contents according to the map layers

Ste 4 : edit the errors and clean the data setStep 5 : convert from digitizer coordinate to map coordinate and store

in a spatial database



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Data Creation


Peter A. Burrough et al

Scannin & Vectorization


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Selection of Paper Map

Define scanning accuracy (DPI) Scanner quality

Separating coverages (layers)

Rasterization where necessary


Scanning Maps


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MarshForest

Color?

DPI?

c mar s

Crop lands


End Product: Vector Polygon of Land Use


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End Product: Vector Lines of Roads


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End Product: Vector Lines of Contours


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End Product: Vector Points of Villages

.


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.


Point Coverage and Attribute Tables


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Polygon Coverage and Attribute Tables


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Line Coverage and Attribute Usage


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Problems in digitizing


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Silver Polygon



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Size 10 x 12Comparison of Raster Cell Size


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Geographical Technologies for Disaster Risk Management IN84.22, Lal SamarakoonTwice the size


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(Polygon) Raster & Vector Attribute Tables


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Conversion of Line Vector to Raster


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What is No Data?


Converted Line Raster Attribute Table

ze x


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(Point) Raster & Vector Attribute Tables


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Direct input


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Built from attribute data e.g. GPS points

Use software extensions for add to GIS database


Aerial Photographs


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21 January Gis

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