1. TERMS, CONCEPTS and DATA TYPES IN GIS Orhan Gündüz

2. Data used in GIS systems are of two major types: 1.Shape data 2.Raster data Shape data is further divided into three: 1.Point data 2.Line/Polyline data 3.Polygon data

3. Point data: 0-D object A point is a combination fo two numbers (X,Y) Represents well locations, crime scenes, cities… Line/polyline data: 1-D object A line is the shortest distance between two points Has a beginning and an ending point Represents streams, boundaries, roads… Polygon data: 2-D object A polygon is a set of points connected by line segments that close back to the first vertex Represents lakes, lots…

4. POINTLINE POLYGON POLYLINE (X,Y) (X 1,Y 1 ) (X n-1,Y n-1 ) (X 1,Y 1 ) (X 2,Y 2 ) (X 1,Y 1 ) (X n,Y n ) (X 2,Y 2 ) left right inside outside * Always follow counter clockwise direction when creating the polygon.

5. Node: A special type of point where at least 3 line segments intersect Defined by a pair of coordinates (X 1,Y 1 ) Pixel: Smallest indivisible element of an image (i.e., pixel in digital pictures) Grid/Grid cell: 2-D object feature that represents a single element of a continuous surface (used in raster data)

6. Symbol: A graphic element that represents features or attributes on a map HospitalAirport Annotation: Text or label graphically pointing a feature ANKARA Gediz River

7. GIS Operations 1.Forward data display (from data to map) 2.Backward data display (from map to data) 3.Point in polygon analysis 4.Line in polygon analysis 5.Polygon overlay 6.Buffers 7.Thematic mapping (data display and capture) 8.Area/Distance calculation operations 9.Geocoding/address matching 10.Network analysis 11.Surface modeling

8. Concept of meta data: “Data about data” An overall description of the contents of the database Documents data Gives description on files, formats, locations, source … Very important

9. Types of Computerized Systems Used in GIS 1.Standalone systems (single PC, local data storage and processing) 2.Networked systems (NT, local processing, centralized data storage, requires authorization) 3.Centralized systems (UNIX, centralized data storage/manipulation)

10. GIS Vector-based GISRaster-based GIS Objects stored as points, lines and polygons Data can be grouped All data have (X,Y) coord. Thematic representation is possible Overlay operations are difficult Boundaries are easily defined Objects stored as grids The higher the resolution, the better the data representation Poor in boundary definition Difficulty in defining vector like objects (eg. A road, a river, a fence) Best for overlay operations Powerful in modeling

11. Topology: The relationship between and among objects Topology is the branch of mathematics which concerns itself with the concepts of: Direction Connectivity Adjacency or contiguity Proximity This design feature allows the computer to know the actual relationship among its graphic parts Topological data structure is based on nodes and edges Commonly used in GIS operations

12. DATA CLASSIFICATION METHODS IN GIS Orhan Gündüz

13. Data in GIS can be classified according to following methods: 1.Natural breaks 2.Quantiles 3.Equal area 4.Equal interval 5.Standart deviation 6.Continuous / discontinuous 7.Normalization

14. NATURAL BREAKS Data is listed from minimum to maximum Boundaries of an abrupt change in data is set a break Data in between breaks are grouped as a unit Statistical methods could also be used to set the breaks Variance minimization is an option QUANTILES Data is broken into intervals with same number of observations Mostly useful for linear data Otherwise can be misleading

15. EQUAL AREA Used to classify polygon data Data divided to form equal area intervals EQUAL INTERVAL Range of equal intervals Ex: If data range is (12…351), then we have a total interval of 339. If divided into 3 intervals, this corresponds to equal intervals of 113. Thus, we obtain: 12-125 125-238 238-351

16. STANDARD DEVIATION Mean of data set is computed Interval breaks are found below and above the mean where these breaks occur at ¼, ½ or 1 standard deviation from the mean Suitable in presenting data that has density information such as population, traffic accidents As data accumulates around the mean and disperse around the mean according to standard deviation, one could see the areas where data accumulates and disperses Continuous / Discontinuous Using upper limits for continuous data Using both upper and lower limits for discontinuous data

17. NORMALIZATION Instead of data value itself, a normalized version is used in representation Normalization is generally done by the sum of all data or the maximum value of the data Data value/ sum(data) * 100