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
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
Evolution of Storage Media
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
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.
ASCII Table
ASCII Table (extend)
Storage Efficiency and Data Compression
 Cartographic
 Need
data sets are typically large
to reconfigure data formats, structures etc.
 Seek
to retain
information content, lose
volume.
 Is
redundancy
necessary?
Rasters vs. Vectors
Storing Coordinates (Vector)
 Physical
Compression
– 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)
 Logical
– Drop
Compression
last two digits (10 ASCII or 2 bytes per
coordinate)
Raster data Compression
 Run-length
 Quad-trees
…
encoding
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
Data Storage Formats for Cartography
- U.S. Geological Survey
USGS DLG format
Data Storage Formats for Cartography
- U.S. Geological Survey
USGS 1:250,000 3-arc second DEM format (1-degree block)
Data Storage Formats for Cartography
- U.S. Geological Survey
USGS 1:24,000 30 meter DEM format (7.5-minute quadrangle)
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
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
–
…
–
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 georeferenced.
 GeoTIFF
is true geographic data format
Finding Existing Map Data
 Map
libraries
 Reference
 State
books
and local agencies
 Federal
agencies
 Commercial
data suppliers e.g.
GeographyNetwork.com, Rand McNally,
Thompson, NAVTEQ, maps.com
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.
Commercial vendors
Federal Data Agencies
 U.S.
Geological Survey (USGS)
 National
 Census
 National
Oceanic & Atmospheric Administration (NOAA)
Bureau
Geospatial-Intelligence Agency (NGA)
 Environmental
 many
more...
Protection Agency (EPA)
National Spatial Data Infrastructure
http://www.fgdc.gov/nsdi/nsdi.html
Geodata.gov
National Spatial Data Clearinghouse
USGS: National Mapping
National Map Viewer
DOQQ (Digital Orthophoto Quarter Quadrangle )
plus DLG streets
DRG (Digital Raster Graphics) plus DLG streets
Seamless data download
Other components of the NSDI
(Portals, standards, services, data)
 Geospatial
Onestop
 Geography
Network
 EROS
 FGDC:
Data Center
Standards
 Alexandria
 State
Digital Library
data centers e.g. Teale in CA
 MapQuest
 NAVTEQ,
etc.
 Counties,
municipalities, universities, tribes, etc.
U.S. Bureau of the Census
National Oceanic and Atmospheric
Administration (NOAA)
Weather and other data
Eros Data
Center
 Distributed
active
archive center
 Sioux
Falls, SD
 Operated
by USGS
US GeoData
ftp access to
DEM
DLG
GNIS
GIRAS
etc.
GNIS
Feature
locations
GIRAS
Land Use and
Land Cover
Data
GIRAS into Arc/Info (GIRASARC)
Terrain data
DEM
DLG Contours
DCW Contours
Next Lecture
Spatial Data Structure