Lecture 2 GIS GeoScience basic

1. Lecture 2 GIS GeoScience basic

2. Earth model Nature surface of earth Spheroid enveloped by sea level Spheroid enveloped by mean sea level Reference ellipsoid

3. Geographical coordinate P(λ,φ) projection Cartesian coordinate system Coordinate system: plane system

4. Coordinate system: Elevation • The distance of point on the surface to mean sea level, is the 3rd dimension of spatial objects. • Absolute elevation and relative elevation • 1985 National Elevation datum: 72.2604.

5. Map projection: Contents • Why is needed map projection • Essential of map projection • Distortion of map projection • Classes of map projection • How to select map projection • Methods of map projection in China

6. Map projection: Why and what • Map projection portrays the surface of the earth or a portion of the earth on a flat surface • Measuring distance ,area and direction are not convenience in position by longitude and latitude • Ellipsoid is not a developable surface • Map projection translates the surface of the earth to a flat surface, and measure and analysis on the flat map is easy

7. Map projection: Concept Earth surface Project surface

8. Map projection: Essential

9. Map projection: Distortions • Map projection always causes distortion on distance, direction, scale and area • Distance distortion • Area distortion • Direction distortion Mollweide Projection Mercator Projection

10. Map projection: Methods Azimuthal projection Project surface Earth surface Conic projection Cylindrical projection

11. Map projection: Classes Azimuthal Projection Geometry Conic Projection Cylindrical projection Method Non-geometry Map projection Equal area projection Distortion Equal angle projection Arbitrariness projection

12. Map projection: geometry projection Vertical axes Tilted axes Horizontal axes Azimuthal Cylindrical Conic

13. Map projection: How to select map projection • Geographical location, shape and range of map field • Scale • Map contents • Published method

14. Map projection in GIS • GIS displays the geographic information in flat surface • Map projection is a key in GIS data acquisition and presentation • GIS has catalogues of projection listed which can be used to choose the appropriate projection

15. Map projection: map projection in China • 1:1000K:Lambert projection • Part of province map and majority of maps with a level scale also adopt Lambert projection • 1:500K、1:250K、1:100K、1:50K、1:25K、1:10K、1:5000 adopt Gauss-Kruger projection

16. Map scale • Portrays the relation of map field to mapping area • Effected map contents, generalize and data accuracy • Scale definition: Scale is the relationship between a distance portrayed on a map and the same distance on the earth Small area: scale is same in each direction Large area: main scale, scale changed with direction

17. Map scale (cont.) • Scale system in China large scale map: 1：500—1：100K medium scale map:1：100K—1：1000K small scale map: 〈1：1000K • Concept of non-scale • Scale and resolution

18. Real world Spatial phenomena and expression Map Spatial data Image Selection Abstract Generalization Relation-ship Features Behavior Position Attribute Relationship observing

19. Type of spatial objects • Spatial objects are classified according to their topological dimension which provides a measure of the way they fill space • Point --- dimension 0 • Line --- dimension 1 • Area--- dimension 2 • Volume--- dimension 3 • Time --- usually considered to be the fourth dimension of spatial objects, although GIS is currently incapable of dealing with it properly • Dimension of spatial objects is related with map scale Cont.

20. Point • A point object has neither length nor breadth and depth • May be used to indicate spatial occurrences or events and their spatial pattern

21. Line • A line has length, but not breadth and depth • Used to represent linear entities that are frequently built together into networks • Also used to measure distance between spatial objects

22. Area • An area object has two dimension, length and breadth, but not depth • Represents area of natural or artificial objects

23. Volume • A volume object has length, breadth and depth • Used to present e.g. mine bodies and buildings or artificial objects

24. Description of spatial objects Spatial objects can be described by the following parameters: Code: to describe type of spatial objects and is sole Position: to present the spatial objects in (x, y) or (λ, φ) Type: entities type, such as: point, line, area and volume etc. Behavior: behavior and functions the spatial objects have Attribute: non-geometry information Remark: to describe the data origin, accuracy etc. Relationship: to represent the relationship of the object with other objects

25. Coding of spatial objects • Attribute • Process: classification  grade  coding • Classification • Definition: gather spatial objects with same attribute • Principle: scientific, systematic, extensible, practical abilities, compatibility • Method: classification according to line or area

26. Coding of spatial objects (cont.) • Grade • Definition: classified the objects according to its features or amounts • Principle: • accuracy • visual • distribution • Lessen the number of grade as possible • Method: nature break, equal interval, RMSE ……

27. Coding of spatial objects (cont.) • Coding: to assign a code to spatial objects • Function: distinguish, classify, sort • Coding principle: sole, rationality, extensive, simplification, application, standardization • Type of code: digital, letter, etc.

28. Code in GIS • Type of code in GIS • Classification code • Identification code • Method of coding • hierarchy • Multi-characters

29. Code of spatial objects: hierarchy • Used to represent spatial objects which have hierarchy or hypotaxis • Strictly hypotaxis relationship • Example:

30. Pipe line electrical wire …… …… Underground electrical wire High-voltage line low-voltage line pole tower frame scale Non-scale Code of spatial objects: hierarchy (cont.)

31. Multi-characters classification coding of river depth navigation Season length breadth 5 ~ 10 m ：1 10 ~ 20 m：2 20 ~ 30 m：3 30 ~ 60 m：4 60 ~ 120 m：5 120 ~300 m：6 300 ~500 m：7 >500m：8 Ever river: 1 Season river: 2 Disappear river:3 < 1 km：1 < 2 km：2 < 5 km：3 < 10 km：4 > 10 km：5 <1 m ：1 1 ~ 2 m：2 2 ~ 5 m：3 5 ~ 20 m：4 20 ~ 50 m：5 >50m：6 Navigation: 1 Non-navigation: 2 Multi-characters classification coding • According to characters of spatial objects • No strict hypotaxis • Be helpful to analyze • Example : River

32. Relationship of spatial objects • Used to describe the inter-relation of objects • Method: • Absolute relation: coordinate, angle, direction, distance • Relatively relation: adjacent, enclosed, conjunction • relatively relation: • Topological relation • Order relation • Measuring relation

33. Relationship of spatial objects (cont.) • The relationship of spatial objects on the map and image can be directly observed, but not be represented directly in GIS • No standard currently, different GIS software may use different methods to describe relation of objects

34. Topological relationship of spatial objects • Topological theory • Topological element：point、line、area • topological relationship： • conjunction:relationship of the different topological elements • adjacent:relationship of the same topological element • enclosed:relationship between area and other elements • hierarchy:hierarchical relationship of the same topological element • Euler formula

35. Advantages and disadvantages of Topological relationship • advantages • Spatial objects can be described by Topological relationship , besides absolute coordinate • Reduce spatial data redundancy • Be easy to overlay • Be helpful to data verification • disadvantages • Complicated in creation • No uniform data structure

36. How to use topological relationship • Application aims • Mapping or simple query, no topological relationship • Spatial analysis, should build topological relationship • serve aims and GIS data structure • area: area-arc, arc-area • network: point-arc, arc-point

37. n: number of node a: number of arc b: number of polygon c: constant c + a = n + b n = 4，a = 4 b = 1，c = 1 n = 6，a = 5 b = 2，c = 1 p=2（number of figure） n = 10，a = 12 b = 3，c = 1 n = 4，a = 5 b = 2，c = 1 Euler formula

38. 1 c B A 2 3 e a D b 7 6 C 5 4 d a: number of node A: number of polygon 1: number of arc Digitization direction of arc Relationship of spatial object: relation table

39. Relationship of spatial objects: relation table (cont.)

40. Spatial auto correlation • The first law in Geography • Type: • Positive auto correlation • Random auto correlation • Negative correlation • Used to describe the dependence of spatial objects

41. Spatial auto correlation: Index Moran I Index: Geary’ c Index:

42. 3 3 1 1 2 1 2 1 2 1 2 3 2 1 2 1 3 1 1 3 2 3 1 3 1 1 2 2 3 2 1 2 2 3 1 3 2 1 2 1 2 1 2 3 3 1 1 3 I = 0.6 C = 0.48 Positive correlation I = -0.15 C = 1.07 Random correlation I = -0.65 C = 1.29 Negative correlation

43. Characters of spatial data • Attribute • Position • Time

44. Type of spatial data • Attribute data • Geometry data • Relative data

45. Map to represent the real world Point position:（x，y） attribute: map symbol Line position: (x1,y1),(x2,y2),…,(xn, yn) attribute: symbol with shape, color, size Area position: (x1,y1),(x2,y2),…,(xi, yi),…,(xn, yn) attribute: symbol, isoline

46. Remote sensing platform sensor

47. 作业 • 简述地图投影选择的一般原则 • 什么是拓扑关系？在GIS中引入拓扑关系有什么有优点和缺点？ • 简述空间数据的自相关特征。 • 简述地图和遥感是如何表达地理对象的。

48. 第二讲结束 谢谢