1. What is Where? Getting Started With Geographic Information Systems Chapter 5

2. A GIS can answer the question: What is where? u WHAT: Characteristics of attributes or features. u WHERE: In geographic space.

3. A GIS links attribute and spatial data u Attribute Data t Flat File t Relations u Map Data t Point File t Line File t Area File t Topology

4. What is a Data Model? u A logical construct for the storage and retrieval of information. u GIS map data structures are map data models. u Attribute data models are needed for the DBMS. u The origin of DBMS data models is in computer science.

5. Historically, databases were structured hierarchically in files... USA CaliforniaOregonNew York Santa BarbaraVenturaContra Costa

6. Most current DBMS is by relational databases. u Based on multiple flat files for records, with dissimilar attribute structures, connected by a common key attribute.

7. Relational Data Bases Purchase Record ItemDatePrice CustomerKey Skate Board2/1/9649.95John Smith42 Baseball Bat2/1/9617.99James Brown978 Patient Record Key Check-inCheck OutRoom No. 422/1/962/4/96N763 782/3/962/4/96N712 Accident Report DateInjuryNameKeyLocation 2/1/96Broken LegJohn Smith4275 Elm Street 2/2/96ConcussionSylvia Jones65412 State Street 2/2/96Cut on EarRobert Doe1232323 Broad Street File

8. A DBMS contains: u Data definition language u Data dictionary u Data-entry module u Data update module u Query language u Report generator

9. Data definition language u Allows the user to establish the structure and names of records and attributes.

10. Data dictionary u Directory of meta-data (information about the data: what data of what types (numerical, text) are available for what areas and time periods?)

11. Data-entry module u Needs to “catch” data-entry mistakes as they happen, based on the dictionary (“What kind of data belongs in this entry?”)

12. Data-update module u Allows corrections and additions or insertions. u Allows new records? u Allows new attributes? u Allows changes in entered values? u Tracks changed values?

13. Query language u Specific operators that allow the user to retrieve information from the data. –“How many records with certain attributes?” –“Create a new attribute by combining attributes.”

14. DBMS queries via the query language u sorting u renumbering u subsetting u searching

15. Command line attribute query compute in states population_density = population / area restrict in states where population_density > 1000 recode population_density = 3 join result with states replace restrict in states where population_density > 100 recode population_density = 2 join result with states replace compute in states where population_density != 3 or 2 population_density = 1

16. Retrieval u The ability of the DBMS or GIS to get back on demand data that were previously stored. u Geographic search is the secret to GIS data retrieval. u Many forms of data organization are incapable of geographic search. u GIS systems have embedded DBMSs, or link to a commercial DBMS.

17. Retrieval Operations u Searches by attribute: find and browse. u Data reorganization: select, renumber, and sort. u Compute allows the creation of new attributes based on calculated values.

18. Spatial Retrieval Operations u Attribute queries are not very useful for geographic search. u In a map database the records are features. u The spatial equivalent of a find is locate, the GIS highlights the result. u Spatial equivalents of the DBMS queries result in locating sets of features or building new GIS layers.

19. Spatial Search u Buffering is a spatial retrieval around points, lines, or areas based on distance. u Overlay is a spatial retrieval operation that is equivalent to an attribute join.

20. Recode OR

21. Data overlay

22. Overlay

23. Types of overlay operations u And u Or u Max u Min u Exhaustive set

24. Buffer + 1

25. Complex Retrieval: Map Algebra u Combinations of spatial and attribute queries can build some complex and powerful GIS operations, such as weighting.

26. Report generator u Allows user to control the format for printing the results of queries. u In a GIS, this parallels the map-creating and editing capabilities of the system.

27. Coming next… u WHY IS IT THERE?