unit 2 AND 3 final lecture f geographic information system and spatial data types.pptx

it is more about GIS and data types, which gives more conceptual awareness, principles, process and methods of using gis as a planning tools and data science to encourage digital planning process and data base about spacial as well as attribute data of the earth and also gives techniques how to aquire datas

1. Principles of Geographic Information System Chapter- II Geographic Information and Spatial Data Types KIRUBEL ENDALE School of architecture and urban planning , Graphics and geo-informatics chair Mobile : [phone] Mail : [email protected]

2. The backbone of GIS is good data accurate enough to accomplish its objectives. Geographic data are organized in a geographic database. There are two important components of this geographic database: geographic position (spatial data)-where is it? attributes or properties (attribute data)-what things are? GIS data types of are grouped into three classes: Spatial data (where?): used to describe location, shape, size, and all kinds features of spatial entities. GIS Data Concepts

3. Non-spatial data (what, when, in what amount?): also called attribute or characteristic data, Also known as descriptive data There are fundamental differences between them: spatial data are generally multi-dimensional and autocorrelated. are positional data Metadata: is data about data and contains information about scale, accuracy, projection/datum, data source, manipulations, how to acquire data . GIS Data Concepts (Contd..,)

4. Geographic phenomena exist in real world and are the study objects of a GIS. Geographic phenomena exist in the real world, everything you see outside is a geographic phenomenon. Some of the things you do not see are also geographic phenomena like temperature. Geographic phenomenon is something of interest that: can be named or described (what?) can be geo-referenced (where?) can be assigned a time (interval) at which it is/was present (when?) Geographic phenomenon can be man-made or natural phenomenon that we are interested in. Geographic Phenomenon

5. There are two groups of geographic phenomena, fields and objects : A geographic field: for every point in the study area, a value can be determined . e.g. temperature, barometric pressure, elevation, etc. Geographic objects: populate the study area, and are usually well distinguishable, discrete, bounded entities . e.g. buildings, geological faults, roads, rivers, etc. Elevation (geographic field) Bridge (geographic object) Geographic Phenomenon (Contd..,)

6. There are two types of geographic fields, discrete fields and continuous fields : Discrete fields: cut up the study space in mutually exclusive bounded parts, with all locations in one part having the same field value . e.g. land classifications, geological classes, soil types, etc. Continuous field: the underlying function is assumed to be continuous. Continuity means that all changes in field values are gradual . e.g. Elevation, temperature, rainfall, etc. Elevation (continuous field) Land Classification (discrete field) Geographic Phenomenon (Contd..,)

7. Nominal data values: provide name or identifier/ categorical data . e.g. geological units, vegetation covers, soil types etc. Ordinal data values: orderly representation as the classes are placed into some form of rank (high-moderate-low) . Interval data values: continuous scale of measurement and a crude representation of numeric data on a scale. e.g. elevation, temperature, etc. Ratio data values: also continuous scale where the origin of the scale is real and not imaginary. e.g. distance measured in meters, rainfall etc . Kinds of Data Values

8. Digital Representation of Data We need to come up with a digital representations of the geographic phenomena in order to store them in a GIS.

9. A digital representation is a model , it is not the real thing. Our representation will never be perfect, some facts will not be found. The choice for a digital representation depends on: The type of phenomenon, From the suitable digital representations you will choose based on two issues: What original raw data is available? What sort of data manipulation does the application want to perform? Computer representations can be divided into two groups: raster and vector-based representations. Digital Representation of Data (Contd..,)

10. A tessellation or tiling is a partition of space into mutually exclusive cells that together make up the complete study area. With each cell some (thematic) value is associated to characterize that part of space. Regular tessellation can be square, hexagonal or triangular in shape. The square shape tessellation is by far the most commonly used and this tessellation is known as raster. Raster Representation

11. In raster representation the field attribute value assigned to a cell is associated with the entire area occupied by the cell. The size of the area that a single raster cell represents is called the raster’s resolution. Examples of raster data representation are aerial photograph, a satellite image, or a scanned map , etc. Regular Tessellation Reality Raster Representation (Contd..,)

12. Two ways to improve on the continuity issue: Make the cell size smaller. Assume that the cell value only represents one specific location and provide a good interpolation function for all other locations. Advantages of regular tessellation: We know how they partition space. We can make computations specific to this partitioning. Fast algorithms. Disadvantages of regular tessellation: Not adaptive to the spatial phenomenon we want to represent. No matter how many cells have the same value, it will store this value for every cell. Raster Representation (Contd..,)

13. Vector representations useful for representing and storing discrete features such as buildings, pipes, or parcel boundaries and can be: Triangulated Irregular Networks (TIN) Point Line Area TIN A TIN is built from a set of measurements for example points of height . These points can be scattered unevenly over the study area, with areas of more change having more points . Vector Representations

14. A Tin is a vector representation Each anchor point has a stored geo-reference. The planes do not have a stored values (like raster cells have) No value is stored for this plane A geo-reference and value is stored for each anchor point Stretched triangles Delaunay triangulation Elevation for TIN construction Vector Representations (Contd..,)

15. ii. Point Points are defined as: single coordinate pairs ( x,y ) when we work in 2D; coordinate triplets ( x,y,z ) when we work in 3D. Arbaminch City can be represented both in point and polygon. HOW?? Used to represent shape and size less single features such as: tree, oil well, poles, fire plugs, etc . iii. Line Used to represent one dimensional objects (roads, railroads, canals, rivers, etc.) Vector Representations (Contd..,)

16. iv. Area (polygon) Used to represent two dimensional features . Polygonal features, such as city boundaries and river catchments can be stored as a closed loop of coordinates. Polygonal data is the most common type of data in natural resource applications. Examples of polygonal data include forest stands, soil classification areas, administrative boundaries, and climate zones . Vector Representations (Contd..,)

17. Raster vs Vector

18. Raster Model Vector Model Advantages: Simple data structure Easy and efficient overlaying Compatible with RS imagery High spatial variability is efficiently represented Simple for own programming Disadvantages: Need high computer storage Errors in perimeter and shape Difficult network analysis Inefficient in projection transformations Loss of information when using large cells Advantages: Compact data structure Efficient for network analysis Efficient for projection transformation Accurate map output. Disadvantages: Complex data structure Difficult overlay operations High spatial variability is inefficiently represented Not compatible with RS imagery Raster vs Vector (Contd..,)

19. UNIT-3 DBMS and spatial referencing

20. Database Management Systems A database can be defined as: A collection of related data/information stored in a structured format . Computerized collection of structured data stored in one or more tables as electronic filing cabinet. A collection of inter-related data stored together to serve one or more applications. A combination of software and hardware that makes it possible and convenient to perform tasks that involve handling large amounts of data.

21. Spatial database is a collection of spatially referenced data that acts as a model of reality. To create and maintain a computer database, you need a database program , often called: Database Management System (DBMS). DBMS is a software package that allows the user to set up, create and maintain a database . GIS is a DBMS specifically designed for processing of spatial and related attribute data. In addition to DBMS, GIS also has many capabilities . A geographic database is a critical part of GIS. Database Management Systems (Contd..,)

22. Handling large amounts of data. Backup and recovery functions to avoid loss of data. Collecting all data at a single location reduces duplication. Maintenance costs decrease because of better organization and decreased data duplication. Applications become data independent so that multiple applications can use the same data. User knowledge can be transferred between applications more easily because the database remains constant. Data sharing is facilitated and a corporate view of data can be provided to all managers and users. Security and standards for data and data access can be established and enforced. Why Use a Database?

23. Spatial Referencing and Positioning

24. Introduction One of the defining features of GIS is the ability to combine spatially referenced data . A frequently occurring issue is the need to combine spatial data : from a given country with global spatial data sets, from different sources, that use different spatial reference systems. To perform these kinds of tasks, GIS users need to understand basic spatial referencing concepts .

25. Reference Surfaces The surface of the Earth is irregular and continuously changing in shape: due to irregularities in mass distribution inside the earth. There is large vertical variations between mountains and valleys of the land masses: this makes it impossible to approximate the shape of the Earth with simple mathematical model. For spatial referencing we need a datum : a surface that represents the shape of the earth .

26. Reference Surfaces Due to practical reasons, two types of spatial positioning are considered: elevations (related to a vertical datum), horizontal positions (related to a horizontal datum). Two main reference surfaces have been established to approximate the shape of the Earth. geoid ellipsoid H h

27. The Geoid - Vertical Datum A reference surface for heights (vertical datum) must be: a surface of zero height, measurable (to be sensed with instruments), level (i.e. horizontal). A surface where water doesn’t flow is a good reference. Geoid is a level surface that most closely approximates the Earth’s oceans . altitudes (heights) are measured from the vertical datums.

28. T o establish the Geoid as reference for heights: the ocean’s water level is registered at coastal places over several years, averaging the registrations largely eliminates variations of the sea level with time, the resulting water level represents an approximation to the Geoid the mean sea level. The Geoid- Vertical Datum The Geoid , exaggerated to illustrate the complexity of its surface.

29. Sea level at the measurement location is affected by: tidal differences, ocean currents, winds, water temperature, salinity . Every country/group of countries has its own mean sea level-local vertical datum . Local vertical datums are parallel to the geoid but offset by up to a couple of meters . Elevations measured from different datums are different. The Geoid - Vertical Datum

30. Ellipsoid- Horizontal Datum A reference surface is required for the description of horizontal coordinates . Ellipsoid is the reference surface for location measurements. t he most convenient geometric reference is the oblate ellipsoid. to project coordinates in a plane, it requires a mathematical representation. Flattening ‘f’ and eccentricity ‘e’ are given as:

31. A horizontal datum is a reference ellipsoid, plus a precisely-measured set of points that establish locations on the ellipsoid. Horizontal datums are realized through large survey networks. Define the shape of the Earth (the ellipsoid.) Define the location of a set of known points – control points – for which the position on the ellipsoid is precisely known. This is the reference surface and network against which all other points will be measured. Defining a Horizontal Datum

32. Basic Coordinate Systems Cartesian coordinates: rectangular coordinate system, using linear distance for defining locations. Geographic coordinates: two-dimensional coordinate system, refer to locations on/close to the Earth’s surface, using angles for defining locations.

33. Latitudes/parallels form circles on the surface of the ellipsoid. the angle between the ellipsoidal normal through a point and the equatorial plane. Longitudes/meridians form ellipses (meridian ellipses) on the ellipsoid. the angle between the meridian ellipse which passes through Greenwich and the meridian ellipse containing the point in question. Basic Coordinate Systems

34. Working with Degrees DMS (degree, minute, second) DD (decimal degree) DDM (degree decimal minute) 1 = 60’ 1’ = 60’’ 1 = 60’ x 60’’ = 3600’’ DMS: 51 29’16’’  DD: 51.4877 29 minutes = 29/60 = 0.4833 degrees 16 seconds = 16/3600= 0.0044 degrees 51 + 0.4833 + 0.0044 = 51.4877 23.2256 = 23 ?’?’’

35. Map Projection A map is a flattened representation of some part of the planet. Mapping onto a 2D mapping plane means: transforming each point on the reference surface with geographic coordinates to a set of Cartesian coordinates representing positions on the map plane. Map projection uses: forward inverse mapping equations.

36. The physical surface used to construct a map: Plane – starts flat, stays flat Developable surface: starts ―rolled, ends flat; geometric shape onto which the Earth surface locations are projected. Projection Developable Surfaces

37. GPS is a worldwide radio-navigation system formed from 24 satellites and their ground stations . Satellites orbit the earth every 12 hours at approximately 20,200 km . Global Positioning System (GPS) GPS uses satellites in space as reference points for locations here on earth. Ground stations help satellites determine their exact location in space .

38. The space segment: consists of a constellation of 24 satellites (and about six "spares"), each in its own orbit. The user segment: consists of receivers , which you can hold in your hand or mount in a vehicle, like your car. The control segment: consists of ground stations (six of them, located around the world) that make sure the satellites are working properly. The master control station at Schriever Air Force Base , near Colorado Springs, Colorado, runs the system. Three Segments of GPS

39. Control Segment Space Segment User Segment Ground Antennas Master Station Monitor Stations Three Segments of GPS

40. Any Questions?

41. THANK YOU