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What is GIS?
Introduction to data
Introduction to data modeling
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A GIS is similar, layering mapped information in a computer to help us view our world as a system
A Geographic Information System is a collection of tools to build, maintain, and use electronic maps and associated databases
It locates:◦ Physical infrastructure, like water and sewer pipes
It locates:
Areas, like land use
It locates:
Incidents, like crime statistics
It locates:
Quantities or densities, like disease ates
It identifies:
More than just maps…
In a GIS, the maps have tables of data behind them.
This means when you combine different maps you combine data to get the information you need.
It allows questions to be asked from the map side or from the database side
Name Jane DoePhone 776-6300School Dist CenterFire Dist No. 12Police Dist CentertownZip 46060
Parcel ID 897-2874A
Owner Jane Doe
Address 110 E Oak
City Anywhere
State Indiana
Zip 46060
Property Value
$72,000
897401
897401
It allows questions to be framed geographically
Left
Right
Inside
Adjacent
Not Adjacent
From
To
Outside
A set of tools for collecting, storing, retrieving at will, transforming, and displaying spatial data from the real world for a particular set of purposes (by Burrough, 1986).
GIS covers three main components: ◦ GIS is a computer system (hardware, software,
procedures or techniques).◦ GIS uses spatially referenced or geographical data.◦ GIS carries out various management and analysis
tasks on these data.
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In short, GIS can be used to add value to spatial data. By allowing data to be organized and viewed efficiently, by integrating them with other data, by analysis and by the creation of new data that can be operated on in turn, GIS creates useful information to help decision making.
A GIS can be described as a form of spatial decision support system.
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Socio-economic/government: health; local government; transportation planning; urban management;
Defence agencies: target site identification; tactical support planning;
Commerce and business: Market share analysis; insurance; retail site location
Utilities: Network management; service provision; telecommunications; emergency repairs
Environmental management: landfill site selection; pollution monitoring; resource management
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GIS is seen as a tool to bring together data and information. ◦ What will be the long-term consequences of
continuing recreational activity for the landscape?◦ What will be the damage from acid rain if a
particular plant continues to operate? ◦ Where is the best location for the reintroduction
of certain bird? ◦ Where should landscape conservation zones be
established?
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What is GIS
Data
Data Modeling
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Data are observations we make from monitoring the real world. GIS is used to help build models where it would be impossible to synthesize the data by any other means.
A GIS populated with data and ideas about how data interact is a spatial model.
Temporal data is used to describe data organized and analyzed according to time,
Thematic data used for data organized and analyzed by theme,
Spatial data for data organized and analyzed by location.
GIS professionals were asked to find appropriate sources of spatial data that could be used to represent some criteria. A range of sources was identified including:◦ Paper maps (for soil type and geology)
◦ Contour maps (for topography)
◦ Ecological field maps (for drainage conditions)
◦ Remote sensing (for land use)
◦ Distributed sensor network (ecology)
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Census and survey data: Collections of related information.
Aerial photographs: It was the first method of remote sensing. It is capturing of images from a position above the Earth. A snapshot of the Earth at a particular instant in time.
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Satellite images are collected by sensors on board a satellite and then relayed to earth as a series of electronic signals.
Some satellites are stationary (geostationary), for example Meteosat, which produce images over Africa along the Greenwich meridian. Other orbit the earth to provide full coverage over some days for example: Landsat and SPOT.
Sensors on board a satellite detect radiation from the Earth. After processing, the images can be used to detect features
not readily apparent to naked eye, such as slight change in moisture content across a field, sediment dispersal in a lake, heat escaping from roof in urban areas.
Scanned images are stored as a collection of pixels, which have a value representing the amount of radiation received by the sensor.
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Establish the purpose the map is to serve; Define the scale at which the map is to produced; Select the features from the real world; Choose a method for the representation of these
features (point, line and areas); Generalize these features for representation in 2D; Adopt a map projection for placing these features
onto a flat piece of paper; Adopt a spatial referencing system to locate these
features relative to each other; Annotate the map with keys, legends and text for
user;
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All GIS software handles spatial data. For example, spatial data about Happy Valley’s weather stations include:◦ Latitude and longitude as a geographical reference. ◦ Connection details such as which service roads, lifts and ski
trails would allow meteorologist access to the weather station.
◦ Non-spatial data such as details of the snowfall, temperature, wind speed and direction.
The functions of GIS: data input, storage, management, transformation, analysis and output.
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Point, line and areas
Topology in GIS describes the geometric characteristics of objects that do not change under transformations such as stretching or bending and are independent of any coordinate system.
It includes three elements:◦ Adjacency: share a common boundary◦ Containment: extension of adjacency and
describe area features which may not wholly contained within another area feature such as inland within a lake
◦ Connectivity: linkages between line features, road.
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Generalization
Projection
Referencing
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Selection: First select the features in the map;
Simplification: Next make a decision to simplify the features;
Displacement: If the features located side by side or lie on top of one another, displace them by a small degree so they are all visible on the map.
Smoothing and enhancement: If source data are collected from a series of sampling points, a smoothing technique may be used to extract shape from the features.
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Principle for map projections:◦ Imagine the beach ball has a hole at the “north pole”
large enough for a light bulb to be inserted, it is transformed into a light fitting. When the light is switched on, an image of the surface is projected onto the walls of the room.
◦ In a circular room, assuming our globe is hanging from the north pole, there will be a continuous picture of the earth. The equator represents line of true scale (not distorted).
◦ In a square room with flat walls, only a part of earth’s surface will be visible on any one wall.
◦ If the room is shaped like a tepee, the line of true is no longer the equators, as in the circular room, but some line of latitude nearer the north pole.
◦ The circular room is equivalent to the family of cylindrical projections.
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Cylindrical
Azimuthal
Conic
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latitude and longitude of Moscow
calculating the latitude
calculating the longitude
What is GIS
Spatial data
Spatial data modeling
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What particular features are found?
What geographical patterns exits?
Where have changes occurred over a given time period?
Where do certain conditions apply?
What will the spatial implications be if an organization takes certain action?
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Raster vs vector
Network
Hierarchical
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Raster DTM (digital terrain modelling) is simply a grid of height value in which each cell contains a single value represented the height of the terrain in that cell. Problems occur with raster DTMs where the terrain is varied.
Vector DTM is the triangulated irregular network (TIN). In vector GIS, a TIN is used to create a DTM from either regular or irregular height data.
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Entity model Cell values File structure
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Run length encoding: reduce data volume on a row by row basis.
Block coding: extend the run length encoding idea to two dimensions by using a series of square blocks to store data.
Chain coding: define the boundary of the entity.
Quadtrees.
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Run length
encoding
Block coding
Chain coding
The quadtree
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A network is a set of interconnected linear features through which materials, goods and people are transported or along with communication of information is achieved. Network models in GIS are abstract representation of the components and characteristics of their real-world counterparts
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What is GIS
What three main components GIS has?
What types of GIS data exist
What is topology in GIS (define 3 types)
What types of operations on GIS exist (list 3 types)
What three types of projection exists
Compare raster and vector approach to modeling
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