gis tutorial 1
DESCRIPTION
GIS Tutorial 1. Lecture 5 Importing spatial and attribute data. Outline. Map projections Coordinate systems GIS data sources Vector data formats Raster data formats. Lecture 5. Map projections. Latitude and longitude. Longitude (meridians). Latitude and longitude. - PowerPoint PPT PresentationTRANSCRIPT
Outline
Map projections
Coordinate systems
GIS data sources
Vector data formats
Raster data formats
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Latitude and longitude° Longitude (prime meridian)0
° Latitude (equator)
0
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Lat/Long coordinates
Degrees, minutes, and seconds (DMS): 40° 26′ 2″ N latitude -80° 0′ 58″ W longitude
Decimal degrees (DD) 1 degree = 60 minutes, 1 minute = 60 seconds 40° 26′ 2″ = 40 + 26/60 + 2/3600 = 40 + .43333 + .00055 = 40.434°
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Lat/long coordinates
Translated to distance World circumference through the poles
is 24,859.82 miles, so for latitude: 1° = 24,859.82 / 360 = 69.1 miles 1′ = 24,859.82 / (360 * 60) = 1.15 miles 1″ = 24,859.82 * 5,280 / (360 * 3,600) =
101 feet
Length of the equator is 24,901.55
miles
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Mercator projection (1569) Conformal projection Cylindrical Parallels and meridians at
right angles Linear scale is constant in
all directions around any point
Preserves angles and shapes of small objects
Distorts the size and shape of large objects
Map projection for nautical purposes
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Hammer – Aitoff (1882-1889) Equal-area Modified azimuthal
projection Good for population
density (world area) Difficult to see some
areas
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Robinson projection (1961) Pseudocylindrical Neither equal area nor
conformal Meridians curve gently,
avoiding extremes Good compromise
projection for viewing entire world
Used by Rand McNally since the 1960s and by the National Geographic Society (1988 and 1998)
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Albers Equal Area Conic projection Scale and shape are
not preserved, distortion is minimal between the standard parallels
Standard projection for British Columbia, U.S. Geological Survey, U.S. Census Bureau
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Projection important Measurements used to make important decisions Comparing shapes, areas, distances, or
directions of map features Feature and image themes are aligned
Los Angeles
New York
Los Angeles
New York
Projection: MercatorDistance: 3,124.67 miles
Projection: Albers equal areaDistance: 2,455.03 miles
Actual distance: 2,451 miles
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Projection not important
Business applications Not of critical importance Concerned with the relative location of
different features
On large scale maps—street maps Distortion may be negligible Map covers only a small part of the earth’s
surface
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Geographic Coordinate System (GCS)
Spherical coordinates
Angles of rotation of a radius anchored at earth’s center
Latitude and longitude
Census Bureau TIGER files
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Rectangular coordinate system
Used for locating an intersection on a flat sheet of graph paper or a flat map
Cartesian coordinates (x,y)
State plane and UTM
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State Plane coordinates Established by the
U.S. Coast and Geodetic Survey in 1930s
Originally North American Datum (NAD 1927)
More recently NAD 1983 and 1983 HARN
Used by local U.S. governments
All positive coordinates in feet (or meters)
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State Plane zones 125 zones
At least one for each state Cannot have zones joined to make larger
regions
Follow state and county boundaries
Each has its own projection: Lambert conformal projection for zones
with east-west extent Transverse Mercator projection for zones
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Universal Transverse Mercator (UTM)
Rectangular coordinate system
Used by U.S. military
Covers entire world
Metric coordinates
Longitude zones are 6° wide
Latitude zones are 8° high
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Coordinate system summary Geographic coordinate system
U.S. Census State plane coordinate system
Local governments U.S. military
Projections defined in ArcCatalog or ArcMap (.prj) files
First file added in a map document sets the projection (others will adjust to it as long as they have a .prj file)
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GIS data sources ESRI U.S. Census USGS and other government sources GDT Dynamap/2000 U.S. Street Data Engineering companies
land surveys, aerial photos, CAD drawings
University Web sites (e.g. Penn State’s PASDA)
Others?
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GIS data sources 30+ million Internet search results
type “GIS data download” or “population China .e00
add the name of the state, county, or city to the search
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GIS departments Web sites Washington, D.C.
dcgis.dc.gov/ Chicago, IL
www.cityofchicago.org/gis
Austin, TX Tip: Search by county name (Travis County,
Texas) http://www.ci.austin.tx.us/development/ ftp://ftp.ci.austin.tx.us/GIS-Data/Regional/coa_gis.html
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ESRI’s Web site http://www.esri.com/data/resources/ge
ographic-data.html
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U.S. Census Bureau Started building a map infrastructure in
the late 1970s and early 1980s Census mapping needs were twofold:
To assign census employees to areas of responsibility, covering the entire country and its possessions
To report and display census tabulations by area, officials determined that the smallest area needed for these purposes is a city block or its equivalent
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U.S. Census Bureau Compiles all line features used to
create a block layer for the entire country
Map features smaller than are the responsibility of local governments deeded land parcels buildings street curbs parking lots others?
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Census TIGER/Line files Topologically Integrated Geographic
Encoding and Referencing files Census Bureau’s product for digital
mapping of the U.S. Available for the entire U.S. and its
possessions Include the following geographic features
roads and street centerlines railroads rivers lakes census statistical boundaries
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TIGER census tracts Statistical boundary (below county
level) between 1,000 and 8,000 people (in
general) 1,700 housing units or 4,000 people homogeneous population characteristics
(economic status and living conditions) normally follow visible features may follow governmental unit boundaries
and other nonvisible features more than 60,000 census tracts in Census
2000
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TIGER census block groups
Subdivision of a census tract 400 housing units, with a minimum of 250
and a maximum of 550 housing units Follow clearly visible features such as
roads, rivers, and railroads
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TIGER census blocks Smallest geographic area for which the
Census Bureau collects and tabulates decennial census information Visible boundaries
street road stream Shoreline
Nonvisible boundaries county, city, neighborhood boundary property line
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U.S. Census Bureau data tables http://factfinder.census.gov
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SF tables comparisons
SF1
Population
Age
Sex
Race
Housing units
FFH
SF3
Income
Educational
attainment
Citizenship
Transportation
Detailed housing
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Census summary Shapefiles downloaded from
www.census.gov or www.esri.com Data tables downloaded from American
Factfinder http://factfinder.census.gov Data joins needed to join SF1 or SF3 to
shapefiles
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ArcInfo coverages Created using ESRI’s ArcInfo software Older format Set of files within a folder or directory called
a workspace Files represent different types of topology or
feature types
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Coverage attribute table
Area and perimeter
Coverage_ and Coverage_ID
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Shapefiles ArcView native format
Minimum files shp–stores feature geometry .shx–stores index of features .dbf–stores attribute data
Additional files .prj–projection data .xml–metadata .sbn and .sbx–store additional indices
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CAD drawings
CAD software Autodesk, AutoCAD (.dwg) Bentley, Microstation (.dgn, .dxf)
Often used by engineering
companies
Better digitizing precision
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Event files Data table that includes map coordinates, such as latitude and longitude or projected coordinates
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Digital file formats TIFF (Tagged Image File Format)
.tif file extension Very high quality images Commonly used in publishing Sizes are large because it is uncompressed
GIF (Graphic Interchange Format): .gif as its file extension. Ideal for schematic drawings that have
relatively large areas with solid color fill and few color variations.
Small file sizes
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Digital file formats JPEG (Joint Photographic Experts
Group): .jpg file extension. Most widely used format for photographs
and other images that have a lot of color variations
Uses file compression at the expense of picture detail, if you specify a lot of compression
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