Lecture Notes for Clarke, K. C. Analytical and Computer Cartography

Lecture 5: Data Storage and Representation

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
• Media have changed
  • Cards
  • Paper Tape
  • Magnetic Tape
  • Fixed & Removable Disk
  • Diskette
  • Exabyte/Zip
  • CD ROM/WORM

Internal Representation

• Physical Storage
• Logical Storage
• Data Format
• Data Structure
• Data Model

Physical Storage

• File System
• Directory
• File
• Bytes
• Bits
• Bit Stream

• Mapping to Bits
  • ASCII
  • Binary
  • Words Register Sizes
  • Integer/Float/Text/Enum
  • Hexadecimal Shorthand
• Mapping to Operations
  • Registers
  • Boolean
  • AND, OR, NAND etc.

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?
• Raster & Vector differences

Storing Coordinates

• Physical & Logical Compression
• Many possible methods, especially for raster data
• Tiling common
• Compression possible e.g. Huffman coding, ZIP

Example using UTM: GIRAS Data

• 4,513,410 m N;587,310 m E; Zone 18,N (32 characters, 15 digits)
• 4513410 587310 (13 digits, one space) Need metadata
• 98 96 7F 0F 42 3F (six bytes)
• Drop last two digits (10 ASCII or 2 bytes per coordinate)

Data Storage Formats for Cartography

Major suppliers of Existing Data are Federal Agencies

USGS

• DLG
• DEM
• DRG
• GIRAS
• GNIS
• DOQ

DOD

• WDB I (1:12M base, 100K points)
• WDBII (1:3M base, 6M Points)
• DCW 1:1M base- 4 CDs, 14 layers DMAs VPF
• DTED
• DFAD

NOS

• NOAA: Weather etc
• Digital Shoreline
• ECDIS
• NGDS: ETOPO5

Digital Image Formats

• NASA: DAACs
• AVHRR & LANDSAT EROS

Industry "Standard" Formats

• RASTER
  • Targa
  • Pict
  • GIF
  • TIF
  • PICT
  • BMP
  • JPEG
• VECTOR
  • DXF
  • HPGL
  • Postscript
  • Arc/Info
  • MicroCAM IDX
• Standard Formats
  • DX-90
  • VPF
  • STDS (ISO 8211)

Keith C. Clarke Last Update 4/15/97 Copyright Prentice Hall (1995)