21 january gis
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Basics of Geo ra hic InformationSystems
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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
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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
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- 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:
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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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?
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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
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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?
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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)
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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
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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
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, ,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
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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.)
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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
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45
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S
S S
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Vector Representation
X-AXIS
Raster Representation
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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
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.
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.
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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
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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?
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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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?
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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
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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.
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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
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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
.
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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
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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
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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
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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
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Scanning Maps
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MarshForest
Color?
DPI?
c mar s
Crop lands
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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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.
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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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(Polygon) Raster & Vector Attribute Tables
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Conversion of Line Vector to Raster
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What is No Data?
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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
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Aerial Photographs
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