0. Lecture 04: Data Storage and Representation & Access to Spatial Data
Geography 128
Analytical and Computer Cartography
Spring 2007
Department of Geography
University of California, Santa Barbara

1. Storage Media
Traditionally, the paper map has performed a storage function for spatial information
Computer cartography requires information to be digital and stored explicitly
Storage is increasingly distributed over networks
Many mapping programs require local storage of data
Cost and size restraints now less important

2. Evolution of Storage Media

3. Physical Storage
Bit - the most basic information unit in a binary system (1 / 0)
1 Byte = 8 bits
Binary (2-based), Decimal(10-based), and Hexadecimal (16-based) System
Binary Operator – AND, OR, NOT
Data on a disk -Sectors, Tracks, Platters
File system – File, Directory

4. Maps as Numbers
Map data is stored in the computer’s memory in a physical data structure (i.e. files and directories).
Files can be written in binary or as ASCII (American Standard Code for Information Interchange) text.
Binary is faster to read and smaller, ASCII can be read by humans and edited but uses more space.

5. ASCII Table

6. ASCII Table (extend)

7. Storage Efficiency and Data Compression
Cartographic data sets are typically large
Need to reconfigure data formats, structures etc.
Seek to retain information content, lose volume.
Is redundancy necessary?

8. Rasters vs. Vectors

9. Storing Coordinates (Vector)
Physical Compression
4,513,410 m N;587,310 m E; Zone 18,N (32 characters, 15 digits)
(13 digits, one space) Need metadata
F 0F 42 3F (six bytes)
Logical Compression
Drop last two digits (10 ASCII or 2 bytes per coordinate)

10. Raster data Compression
Run-length encoding
Quad-trees …

11. Data Storage Formats for Cartography - U.S. Geological Survey
DLG – Digital Line Graphs (1:24,000; 1:100,000; 1:2,000,000)
DEM – Digital Elevation Model (1:24,000; 1:250,000)
GIRAS – Land-use and Land-cover Digital Data (1:100,000; 1:250,000)
GNIS – Digital Cartographic Text

12. Data Storage Formats for Cartography - U.S. Geological Survey
USGS DLG format

13. Data Storage Formats for Cartography - U.S. Geological Survey
USGS 1:250,000 3-arc second DEM format (1-degree block)

14. Data Storage Formats for Cartography - U.S. Geological Survey
USGS 1:24, meter DEM format (7.5-minute quadrangle)

15. Data Storage Formats for Cartography - CIA World Data Bank
WDB I (1:12M base, 100K points)
WDBII (1:3M base, 6M Points)
DCW 1:1M base- 4 CDs, 14 layers DMAs VPF

16. Data Storage Formats for Cartography - Industry “Standard” Vector Formats
Vector formats are either page definition languages or preserve ground coordinates.
Page languages are HPGL, PostScript, and AutoCAD DXF.
Proprietary GIS Formats
Arc/Info, ArcGIS
MapInfo …

17. Data Storage Formats for Cartography - Industry “Standard” Raster Formats
Most raster formats are digital image formats.
Most GISs accept TIF, GIF, JPEG or encapsulated PostScript, which are not geo-referenced.
GeoTIFF is true geographic data format

18. Finding Existing Map Data
Map libraries
Reference books
State and local agencies
Federal agencies
Commercial data suppliers e.g. GeographyNetwork.com, Rand McNally, Thompson, NAVTEQ, maps.com

19. Existing Map Data
Existing map data can be found through a map library, via network searches, or on media such as CD-ROM and disk.
Many major data providers make their data available via the World Wide Web, a network of file servers available over the Internet.
GIS vendors package data with products.

20. Commercial vendors

21. Federal Data Agencies U.S. Geological Survey (USGS)
National Oceanic & Atmospheric Administration (NOAA)
Census Bureau
National Geospatial-Intelligence Agency (NGA)
Environmental Protection Agency (EPA)
many more...

22. National Spatial Data Infrastructure

23. Geodata.gov

24. National Spatial Data Clearinghouse

25. USGS: National Mapping

26. National Map Viewer

27. DOQQ (Digital Orthophoto Quarter Quadrangle ) plus DLG streets

28. DRG (Digital Raster Graphics) plus DLG streets

29. Seamless data download

30. Other components of the NSDI (Portals, standards, services, data)
Geospatial Onestop
Geography Network
EROS Data Center
FGDC: Standards
Alexandria Digital Library
State data centers e.g. Teale in CA
MapQuest
NAVTEQ, etc.
Counties, municipalities, universities, tribes, etc.

31. U.S. Bureau of the Census

32. National Oceanic and Atmospheric Administration (NOAA) Weather and other data

33. Eros Data Center Distributed active archive center Sioux Falls, SD
Operated by USGS

34. US GeoData ftp access to DEM DLG GNIS GIRAS etc.

35. GNIS Feature locations

36. GIRAS Land Use and Land Cover Data

37. GIRAS into Arc/Info (GIRASARC)

38. Terrain data DEM DLG Contours DCW Contours

39. Next Lecture
Spatial Data Structure