Nature of Geographic Data

Transcription

1 Stefanakis, E., Geographic Databases and Information Systems. CreateSpace Independent Publ. [In English], pp.386. Get a copy from Amazon Chapter 1 Nature of Geographic Data Emmanuel Stefanakis

2 The nature of geographic data Geographic data special category of data distributed in space changes over time physical objects (e.g., house, road, lake, human, forest, etc.) geogr. phenomena (e.g., temperature, car accidents, humidity etc.) Geographic data administrative units (e.g., municipality, army camp, etc.) derived info (e.g., poverty level, land uses, etc.) 2

3 Reality and Mini-world Reality is very complicated Reality To describe the reality We usually focus into a small part of it called Mini-world Mini-world 3

4 Reality and Mini-world Miniworld of Cadastre example... B N E C F Y Company ltd X A D G 4

5 Reality and Mini-world The miniworld split into small units (entities) consists of entities distinct and interrelated Entity a unit or object with physical or conceptual existence Reality Mini-world 5

6 Reality and Mini-world Miniworld of Cadastre example... B N E C F Y Company ltd X A D G 6

7 B Reality and Mini-world Y N X E C F Company ltd A D G Reality Mini-world Entities (units or objects) 7

8 B Reality and Mini-world Y N X E C F Company ltd A D G Reality Mini-world Attributes Entities (units or objects) Entity Relationship 8

9 Entities An entity is described by a set of properties (attributes) e.g., a house has an address, date of construction, number of rooms, etc. Attributes are classified and form entity dimensions identidier (id) Geographic Entity spatial thematic 9

10 Entities and attributes Identifier (id)... a reference to entities arbitrary names, geogr. names, numeric codes the system assigning id s guarantees... uniqueness, stability, precision, consistency identidier (id) Geographic Entity spatial thematic 10

11 Entities and attributes Thematic dimension all non-spatial properties of an entity application dependent multimedia objects (sound, pictures, movies) identidier (id) Geographic Entity spatial thematic 11

12 Entities and attributes Spatial dimension identidier (id) Geographic Entity spatial Geographic Entity Geographic position Geometry Graphical Parameters Spatial relationships spatial thematic 12

13 Entities and attributes Spatial dimension spatial properties describe entity s geographic position where is it? (coordinates, address, etc.) geometry which are its geometric properties? (shape, area...) graphical parameters how is it represented in a graphical representation? (map symbols, etc.) spatial relations with other entities which are its topological, metric and direction relationships with other entities? (overlaps, near, north of, etc.) 13

14 Reality and Mini-world Miniworld of Cadastre example... B N E C F Y Company ltd X A D G 14

15 Spatial Relations Metric Relations Direction Relations Topologic Relations B N E C F Y Company ltd X A D G 15

16 Spatial Relations Topologic Relations (Egenhofer s model) A is disjoint from B A contains B A meets B A covers B A overlaps B A is covered by B A is inside B A is equal to B 16

17 The nature of geographic data Dynamic geographic entities Attributes (spatial and thematic) change over time if considered: dynamic world / if not: static world Άνδρος Γυάρος Τήνος Κέα Μύκονος Σύρος Ρήνεια Κύθνος Δήλος Sailing in the Aegean Sea 17

18 The nature of geographic data Dynamic geographic entities space-time (chorochronos) 1 h 10 min 1 h 00 min 0 h 50 min 0 h 40 min 0 h 30 min 0 h 20 min Άνδρος 0 h 10 min 0 h 00 min Κέα Γυάρος Τήνος Μύκονος Sailing in the Aegean Sea Κύθνος Σύρος Ρήνεια Δήλος 18

19 The nature of geographic data Geographic entities (properties) change over time ( chorochronos ) are accompanied with errors (data quality) identidier (id) Geographic Entity Chorochronos Data quality spatial thematic 19

20 The nature of geographic data Dynamic geographic entities two types of changes over time... life change changes that affect the existence motion change changes in either spatial or thematic properties life and motion of geographic entities 20

21 The nature of geographic data Life and motion of geographic entities appear merge disappear split thematic change position change form change thematic and position change position and form change thematic and form change 21

22 The nature of geographic data Temporal relationships between dynamic entities numerous and complex time is linear and continuous for a pair of instant phenomena which one occurs first? for a pair of phenomena with duration do they overlap? 22

23 The nature of geographic data Temporal relationships Temporal relation Definition Α before Β A t B Α equal to Β A B Α meets Β t A t B Α during Β A B Α overlaps Β t A B t Α ends Β B A Α starts Β A B t t 23

24 The nature of geographic data Data quality values assigned to an entity properties are collected by measurements those measurements are accompanied by errors data quality offers a measure of how reliable is data so that it is handled effectively 24

25 Measurement Assignment of values to the attributes of geographic entities VALUES ATTRIBUTES 25

26 Levels of Measurements There are four levels/scales of measurements NOMINAL ORDINAL CARDINAL RATIONAL 26

27 Levels of Measurements NOMINAL Assigns identifiers or names ORDINAL Notion of ordering: SOIL: 1:dry, 2:little wet, 3:wet, 4:very wet CARDINAL (judge about differences) Arbitrary origin arbitrary unit A: 10 o Celsius; B: 20 o ; C: 30 o ; D: 45 o (twice as warm???) RATIONAL (extract ratios) Absolute origin arbitrary unit A: 50Kgr ; B: 100Kgr (double weight) 27

28 Levels of Measurements Marathon Race. NOMINAL men Σοφία Mary Κώστας John women Ελένη Helen Ιωάννα Joanne Παντελής Dennis wearing red shirt Σπύρος Tom 28

29 Levels of Measurements Marathon Race. ORDINAL Order Women Men 1 st Joanne Dennis 2 nd Mary Tom 3 rd Helen John 29

30 Dennis Tom Joanne John Mary Helen Levels of Measurements Marathon Race. CARDINAL 12:00 12:05 12:10 12:15 30

31 Dennis Tom Joanne John Mary Helen Levels of Measurements Marathon Race. RATIONAL 0:00 /.../ 2:20 2:25 2:30 2:35 31

32 Levels of Measurements Level Properties Valid operations Nominal Identification, no subject of any ordering equation (=) Ordinal Ordering without any notion of spaces between the classes. ordering (>, <) Cardinal Contnuous measurements, with specific addition, substraction, distances from an arbitrary origin. scale change Rational Contnuous measurements, with specific Multiplication, division distances from an absolute origin. (rates) 32

33 Stefanakis, E., Geographic Databases and Information Systems. CreateSpace Independent Publ. [In English], pp.386. Get a copy from Amazon Chapter 1 Nature of Geographic Data Emmanuel Stefanakis