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 data sets are typically large Need 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) – (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)

Raster data Compression Run-length encoding Quad-trees …

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, 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 geo- referenced. GeoTIFF is true geographic data format

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

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 Oceanic & Atmospheric Administration (NOAA) Census Bureau National Geospatial-Intelligence Agency (NGA) Environmental Protection Agency (EPA) many more...

National Spatial Data Infrastructure

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 Data Center FGDC: Standards Alexandria Digital Library State 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

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

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