What is GIS? Introduction to data. Introduction to data modeling

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2 What is GIS? Introduction to data Introduction to data modeling 2

3 A GIS is similar, layering mapped information in a computer to help us view our world as a system

4 A Geographic Information System is a collection of tools to build, maintain, and use electronic maps and associated databases

5 It locates: Physical infrastructure, like water and sewer pipes

6 It locates: Areas, like land use

7 It locates: Incidents, like crime statistics

8 It locates: Quantities or densities, like disease ates

9 It identifies:

10 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.

11 It allows questions to be asked from the map side or from the database side Parcel ID A Owner Jane Doe Address 110 E Oak City Anywhere State Indiana Zip Property $72,000 Value Name Jane Doe Phone School Dist Center Fire Dist No. 12 Police Dist Centertown Zip

12 It allows questions to be framed geographically Outside From Not Adjacent Right Left Inside To Adjacent

13 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. 13

14 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. 14

15 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 15

16 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? 16

17 What is GIS Data Data Modeling 17

18 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. 18

19 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) 19

20 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. 20

21 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. 21

22 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; 22

23 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. 23

24 Point, line and areas 24

25 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. 25

26 Generalization Projection Referencing 26

27 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. 27

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29 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. 29

30 Cylindrical Azimuthal Conic 30

31 latitude and longitude of Moscow calculating the latitude calculating the longitude 31

32 What is GIS Spatial data Spatial data modeling 32

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34 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? 34

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36 Raster vs vector Network Hierarchical 36

37 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. 37

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39 Entity model Cell values File structure 39

40 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. 40

41 The quadtree Run length encoding Block coding Chain coding 41

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43 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 43

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45 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 45