WFM 6202: Remote Sensing and GIS in Water Management

1. [Part-B: Geographic Information System (GIS)] WFM 6202: Remote Sensing and GIS in Water Management Lecture-4(b): Geo-Database Akm Saiful Islam Institute of Water and Flood Management (IWFM) Bangladesh University of Engineering and Technology (BUET) December, 2007

2. Lecture Topic • Understand basic Geodatabase concepts and structure • Know the advantages in using the Geodatabase format • Managing a GeoDatabase • Creating GeoDatabase

3. AS400 Database Access Database Tabular Data Spatial Data First Generation Storage/Linking • Tabular/Spatial data is linked outside the database • Links occur using unique IDs….Parcel Numbers • Storage is still in separate locations

4. Tabular Data Spatial Data Second Generation Storage/LinkingGeodatabases • Tabular/Spatial data is stored/linked in a single location!!

5. Benefits of a GeoDatabase • Spatial & attribute data integrity • Intelligent Behavior • Centralized Data Storage • Increased Performance • Advanced Analysis Capabilities • Multi-user editing (SDE format)

6. Benefits of Migrating to a GeodatabaseData Integrity • Maintain tabular data more efficiently • Reduce typological data errors • Maintain spatial data more efficiently • Reduce spatial errors Pro-West & Associates

7. What is a Geodatabase? • A spatial and attribute data container • Relational database management system (RDBMS) • Maintains data integrity • Apply Rules and Behavior • Native data format for ArcGIS Relational Database - A method of structuring data as collections of tables that are logically associated to each other by shared attributes. Any data element can be found in a relation by knowing the name of the table, the attribute (column) name, and the value of the primary key.

8. 2 Types of Geodatabase • Personal Geodatabase • Stand alone PC, MS Access database • Supports individual and small groups on moderate size datasets • Enterprise Geodatabase • Exists on underlying RDBMS through Spatial Database Engine (SDE) e.g. SQL Server • Usually runs on a dedicated server • Supports many users and massive datasets • Supports raster datasets

9. SDE SQL GIS View/Analyze Interpreter Data Storage Two types of GeoDatabases • Personal • Access • Multi-user • SDE

10. The Personal GeodatabaseIt’s not Scary! • Stores spatial and tabular data in an Access database format • Sets the stage for future SDE geodatbase migration • Edit in ArcView, ArcEditor or ArcInfo

11. Geodatabase Features Feature Dataset • Contains tables, feature classes, feature datasets, topology rules, etc. Topology Feature Classes Tables

12. Geodatabase Elements Geodatabase Feature data set Geometric network Feature class Relationship class Table Annotation class

13. GeoDatabase (GDB) structure • Stores • Feature datasets • Feature classes • Tables • Raster • More • A unique structure within the GDB

14. Feature Dataset • Contains Feature Classes • Must have same coordinate system • Required for Topology • Behavior relationships between feature classes.

15. GDB Objects: Feature Dataset • A collection of feature classes • Environment for spatial reference • Environment for topology • Environment for coincident geometry and linked annotation • Feature classes inherit spatial reference • Data loaded are projected on the fly, if necessary

16. Feature Class • Stores a single feature type • Point, Line, Polygon • Can be standalone or member of a Feature dataset Feature Dataset Feature Class Stand Alone

17. GDB Objects: Feature Class (FC) • A collection of features • Each feature class has one geometry type (point, multi-point, line, polygon) • Can be stored in a feature dataset or ‘stand-alone’ • Attributes are stored with coordinate data in one table

18. Spatial Reference A

19. Coordinate domain • Extent of available coordinates • Min and max X,Y coordinates • Precision = storage units per map unit • Example, 1000 mm per meter • Make sure it covers study area • Allow for growth • ArcCatalog default • Import: data plus room for growth • Set your own • Import from existing data • Type in extent for study area 2.14 billion storage units

20. Domain • A property of a feature dataset or feature class (cannot change once set)

21. Domains • Spatial • Attribute • Range of values (e.g., 0-100) • Coded values (e.g., 1 = potatoes 2 = wheat)

22. The Spatial Domain • The Geodatabase stores all geometry coordinates as positive integers • Faster Display, Processing, and Analysis • Better Compression (DBMS only) • Efficient for managing topologic relationships • Limited to 2,147,423,647 storage units. • 2.14x109 meters, or miles, or inches, or ...

23. Accuracy and Precision • Accuracy in the Data • Scale of source map scale will determine accuracy* • 1:600 (1”=50’) ± 1.7 feet • 1:1,200 (1”=100’) ± 3.33 feet • 1:2,400 (1”=200’) ± 6.67 feet • 1:4,800 (1”=400’) ± 13.33 feet • 1:24,000 ± 40.00 feet • Precision • Ability to store the accuracy • Significant digits • Single precision 6-7 precise digits • Double precision 13-14 precise digits • Geodatabase 0-10 precise digits

24. 2,147,423,647 2,147,423,647 0 0 OFF LIMITS Example: Spatial Domain • All GIS Features Must Fit Within this Positive, 32-bit Integer Space. The Database’s Spatial Domain

25. Standard Fields • Feature classes have default fields • ObjectID – unique identifier • Shape – contains coordinates of feature • Area – automatically calculated and maintained for polygons • Shape_Area (Personal GDB) • Length – automatically calculated and maintained for lines and polygons • Shape_Length (Personal GDB)

26. Spatial Reference • Property of a feature class or feature dataset • Components • Coordinate system • Coordinate domain • Permanent after definition is saved • Warning: it may look like you changed the coordinate system, but you can’t and don’t try. It messes things up! • See next slide for more information

27. Storing Feature Coordinates Two important considerations when storing feature coordinates in a Geodatabase: • All data is stored as positive, 32-bit integers (Spatial Domain) • All data must maintain a Coordinate Precision.

28. Coordinate Precision • The geodatabase converts all coordinates into 32-bit Storage Units. • Storage Units are the smallest measurable unit that can be stored in a Geodatabase. • Precision is used to convert coordinate system units into storage units.

29. X = 123.456789Precision =1000 Floating Point Coordinate in ArcGIS (123.456000) Multiply by Precision 123.456789 × 1000 Divide by Precision 123456 ÷ 1000 Integer Storage Unit in a Geodatabase(123456) Example: Coordinate Precision • Precision is a Scale Factor • Used to preserve decimal places before rounding • Larger precision preserves more digits

30. Coordinate System Units Precision Storage Units = Example: Precision Preservation

31. Topology Objects • Maintain data integrity • Within feature class • Between feature class • Feature Dataset required • Functionality • Display Topology Errors • Select and Correct Errors • Validation • Regarding map features, topology is relationship between features connectivity and adjacency. • Geodatabase topology provides tools to ensure integrity of spatial data.

32. Selected Topology Rules • 25 available topology rules • 2 Rules currently applied • Must Not Overlap • Must Not Have Gaps

33. File Management • Compacting the Personal Geodatabase • Reduces file size • Procedure • In ArcCatalog, right click on the .mdb file • Select the Compact Database option in the context menu

34. Reference Data Locations • Proscribed by the Standard for Geospatial Dataset File Naming • http://dlnt20.fsa.usda.gov/scdm/DP/Parent3.htm • Standard folder structure on shared f: drive • Geodata – top level geospatial data folder • Local Geodata Administrators have authority to create, delete, and change folders, but only as outlined in the standards document.

35. Data Management File Naming Standards • The current standard has 23 common geospatialdataset categories such as soils that consist of 1 or more geospatial datasets. <disk drive>: geodata plants <geospatial dataset category (directory / folder)> soils <geospatial dataset category (directory / folder)> <geospatial dataset> soil_a_ks057 soil_p_ks057 <geospatial dataset> soil_l_ks057 <geospatial dataset> topographic_images <geospatial dataset category (directory / folder)>

36. Data Management File Naming Standards cont. • Elements of a file name Location: Alpha or numeric FIPS code soil_a_ks057 Feature category Feature type: a-polygon, l-line, p-point, t-table, i-image, etc. • A geospatial dataset file name should: • be less than 30 characters long • consist of lower case a-z and numerals 0-9 • first character always a-z

37. Data Storage and Backup • Shared data in a service center must be on the f: drive. • Personal data can be stored on the c: drive or h: drive. • c: drive is not routinely backed up. • h: drive should contain important working files that can be routinely backed up. • Local Geodata Administrators are responsible for ensuring backups are routinely being made of specific directories. • Large, easily replaced datasets should not be routinely backed up because they can be obtained again. • Files and directories that change regularly should be routinely backed up.

38. GDB Design • A critical step • UML modeling for ArcGIS • IBM Rational Rose • MS Visio • Class diagrams

39. Managing Your GDB • ArcCatalog is your main tool to manage the schema • Construction of component parts • Organization of those parts • Properties for the parts • Many capabilities are available • Some are not on the default GUI

40. Reading Schemas Most data access technologies provide a way for you to query the schema of a database, and obtain information about the tables, stored procedures, data types, users, and other content of a database. Logical Structural

41. Creating a GDB • Personal • Use ArcCatalog • Multi-user • Must be done at the system level A

42. Creating a new personal geodatabase • Open ArcCatalog • Choose a folder location • Right click: Choose New < Personal Geodatabase

43. Creating Feature Datasets Right click your geodatabase Choose: New < Feature Dataset

44. Creating an empty feature class • Two locations available: stand-alone and within a feature dataset A

45. Creating a feature dataset A

46. Creating Feature Datasets Right click your geodatabase Choose: New < Feature Dataset

47. Feature Datasets: Setting the spatial reference • Set the Projection • Set the Domain • Precision • Extent http://arcscripts.esri.com/ : Search on Spatial Domain

48. Import existing data • Navigate to the feature dataset or geodatabase icon in ArcCatalog • Right Click • Choose Import Use this to import any existing format!

49. Subtypes & Domains • Subtype: • Distinguish features within a single layer • Maintain different domains within the same field • Need ArcEditor or ArcInfo • Domain: • Identify & constrain attribute values • Can utilize in ArcView

50. Subtypes & DomainsParcels • Example • Subtype: Boundary Line • Domains: • ROW Type