Geographic Coordinates
GIS 1
Geographic Coordinate System
• Spherical coordinates
based on angles of
rotation of a radius
anchored at earth’s
center
• Latitude and longitude
• Used by many world
and federal agencies
(e.g. U.S. Census
Bureau)
GIS 2
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°
GIS 3
Lat/long coordinates
Translated to distance
•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
World circumference through the poles is
24,859.82 miles
Length of the equator is 24,901.55 miles
GIS 4
Longitude lines
0 ° Longitude (prime meridian)
GIS 5
Prime Meridian (Greenwich
England)
GIS 6
Latitude lines
0 ° Latitude (equator)
GIS 7
Latitude and longitude
Coordinates
Pittsburgh, PA USA
40
-80
GIS 8
Map Projections
GIS 9
Map projections
•Way to represent the curved surface of the
Earth on the flat surface of a map
•Each map projection has advantages and
disadvantages
•depends on the scale of the map
•purposes for which it will be used
•some projections are good for
-small areas
-areas with a large east-west extent
-areas with a large north-south extent
GIS 10
Map projections
Planar
Cylindrical
Conic
http://www.nationalatlas.gov/articles/mapping/a_projections.html#two
GIS 11
Conformal projection
• Cylindrical projection
• Parallels and meridians at right
angles
• Preserves angles and shapes of
small objects
• Distorts the size/shape/area of
large objects
• Seldom used for world maps
Example: Mercator projection
(1569)
GIS 12
Equivalent Projection
• Conic projection
• Preserves accurate area
• Scale and shape are not
preserved
• Standard projection for
U.S. Geological Survey, U.S.
Census Bureau
Example: Albers Equal Area
GIS 13
Compromise Projections
• Good for viewing entire
world
• Neither equivalent nor
conformal
• Meridians curve gently
• Doesn’t preserve properties,
but “looks right”
• Used by Rand McNally and
the National Geographic
Society
Example:
Robinson projection (1961)
GIS 14
When projection is important
• Small-scale maps
-Comparing shapes, areas, distances, or directions of map features
-Natural appearance desired
New York
Los Angeles
Projection: Mercator
Distance: 3,124.67 miles
New York
Los
Angeles
Los Angeles
Projection: Albers equal area
Distance: 2,455.03 miles
Actual distance: 2,451 miles
GIS 15
When projection is not important
•Many business, policy, and management
applications
-Concerned with the relative location of different features
•On large scale maps
-Error is negligible
GIS 16
Rectangular Coordinate
Systems
GIS 17
Rectangular coordinate systems
UTM (U.S. military)
State Plane (local U.S. governments)
• Cartesian coordinates (x,y)
GIS 18
Universal Transverse Mercator (UTM)
• Developed by U.S.
Army Corps of
Engineers (1940s)
• Covers world, 80°S
to 80°N
• Metric coordinates
• Not a single
projection but 60
tuned Transverse
Mercator
projections
GIS 19
State Plane Coordinate System
• Established by the
U.S. Coast and Geodetic
Survey in 1930s
• Used by local U.S.
governments
• Rectangular coordinates (all
positive coordinates in feet or
meters)
• Originally North American
Datum (NAD 1927)
• More recently NAD 1983 and
1983 HARN
GIS 20
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 zone has its own, tuned projection
-Lambert conformal projection for zones with east-west
orientation
-Transverse Mercator projection for zones with north-south
orientation
GIS 21
State Plane zones
GIS 22
Pittsburgh Neighborhoods as State Plane
Coordinates
•1983, Pennsylvania South, Feet
GIS 23
ArcGIS projection tip
• GIS map layers in different projections have different coordinate systems
and thus will not overlay each other unless they have spatial reference
data in a .prj file
• Assign projections according to the agency
U.S. Census Files
•
•
•
Federal agency
Block groups
Geographic coordinate system
City of Pittsburgh
• Local planning agency
• Sidewalks
• State plane coordinate system
GIS 24
ArcGIS projection tip
• The first layer added in ArcMap sets the “map projection”
• Additional layers will overlay properly as long as the correct .prj file is
included
• Example: Sidewalks added first (state plane), block groups match even
though they are geographic coordinate system (gcs) projection
GIS 25
GIS Data Sets
GIS 26
GIS Data Sets
• ArcInfo Coverages
• ArcView Shapefiles
• Annotation Layers
• CAD Files
• Aerial Photos
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 27
ArcGIS
•Integrated collection of GIS software products
•ArcGIS framework deploys GIS functionality
and business logic wherever it is needed—in
desktops, servers (including the Web), or
mobile devices.
-Desktop GIS (ArcView, ArcInfo, ArcReader,
ArcEditor, ArcGIS Extensions, ArcExplorer)
-Server GIS (ArcIMS, ArcGIS Server)
-Mobile GIS (ArcPAD)
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 28
ArcInfo
GIS 29
ArcInfo Coverages
AAT
ARC
BND
CNT
PAL
PAT
TIC
DBF
Arc Attribute Table
Arc coordinates and topology
Coverage minimum and maximum coordinates
Polygon centroid table
Polygon topology
Polygon/Point Attribute Table
Tic coordinates and Ids
Database Table
GIS 30
ArcInfo Coverages
• Advantages
-Many feature types
• Disadvantages
-Cannot edit in ArcMap
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 31
Coverage Attribute Table
• Polygon Coverage
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 32
Coverage Attribute Table
• Point Coverage
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 33
Coverage Attribute Table
• Line Coverages
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 34
ArcInfo Export files
• .e00 export exchange file
• ArcToolbox translates into ArcGIS
• Creates Coverages
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 35
ArcView Shape Files
Advantages
•heads-up digitizing and editing
•less storage/rapid display
•can convert from ArcInfo coverage and back
•can export to CAD
Disadvantages
•one feature type
•no area or perimeter
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 36
ArcView Shape Files
From 3 to 5 Files
•.shp - stores feature geometry
•.shx - stores index of features
•.dbf - stores attribute data
•.sbn and .sbx - store additional indices
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 37
ArcView Shapefiles
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 38
Annotation Layers
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 39
Annotation Layers
• Separate independent layers
• Can be turned on/off
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 40
CAD Files
Why CAD Drawings?
• Better Precision for Digitizing
-AutoCAD
-Microstation
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 41
Aerial Photos
Combining Grid and Vector Maps
Copyright – Kristen S. Kurland, Carnegie Mellon University
GIS 42
XY Event Tables
GIS 43
XY Data (Event Files)
Data table that includes map coordinates, such as latitude and
longitude or projected coordinates
GIS 44
Event Files
GIS 45
Exporting Event Files
GIS 46
GIS Data Sources
GIS 47
Common Sources
•U.S. Census Bureau
•Geospatial One Stop
•U.S. Geological Survey
•Esri
•Historic websites
•Colleges and universities
•International sites
•State agencies
•Local agencies or engineering firms
GIS 48
U.S. Census TIGER/Line® Files
http://www.census.gov/geo/www/tiger/
Topologically Integrated Geographic
Encoding and Referencing files
-Census Bureau’s product for digital mapping of
the U.S.
-TIGER maps are available for the entire U.S.
and its possessions
GIS 49
Census TIGER/Line® Files
GIS 50
State Census Tracts (2000)
County sub-divisions
Between 1,000 and 8,000 people or 1,700 housing units and 4,000 people
Homogeneous population characteristics (e.g. economic and living)
Normally follow visible features
May follow government boundaries or other non-visible features
GIS 51
County Census Tracts (2000)
GIS 52
City Census Tracts (2000)
GIS 53
Census Block Groups (2000)
Census tract sub-divisions
400 housing units, with a minimum of 250 and maximum of 550
Follow visible features such as roads, rivers, and railroads
GIS 54
Census Blocks (2000)
Smallest geographic area for which the U.S. Census Bureau collects and
tabulates decennial census information
Block boundaries are visible (street, road, stream, shoreline, etc) or nonvisible (county or city limits, property lines, etc.)
GIS 55
U.S. Census data tables
American FactFinder
GIS 56
http://factfinder.census.gov/
GIS 57
2000 Summary File Tables
Summary File 1 (SF1)
Short form, entire population
• Population
• Age
• Sex
• Race
• Families
• Households
• Housing units
Tracts, block groups,
blocks
Summary File 3 (SF3)
Long form, 1 in 6 households,
randomly
• Income, poverty
• Educational attainment
• Citizenship
• Employment, workplace,
disability
• Transportation, travel time to
work
• Detailed housing attributes,
housing value, residency 5
years previous
• Languages spoken, ancestry
Tracts, block groups
GIS 58
http://factfinder2.census.gov/main.html
GIS 59
2010 Data Release Schedule
http://www.census.gov/population/www/cen2010/glance/
GIS 60
Data Ferret
http://dataferrett.census.gov/
GIS 61
Spatial data infrastructure
•Federal Geographic Data Committee
-Established by presidential order
-Responsible for standards, policies, web portals
-Geospatial One Stop, http://gos2.geodata.gov
Base maps and spatial data produced
by governments for the public good
Non-rivalrous and non-excludable
consumption
Widely-used structures needed for
society and enterprises to function
GIS 62
Physical features:U.S. Geological Survey
• National Map
Orthoimagery,
replacing the Digital
Orthophoto
Quadrangles
-High-resolution, seamless
images in UTM
coordinates
-Rectified to remove
distortions
-1m resolution with 0.5 m
or 1 ft in urban areas,
natural color
GIS 63
Physical features:U.S. Geological Survey
• National Elevation
Data set (NED)
-Replaces the Digital
Elevation Model
(DEM)
-Seamless raster
map with 30m
resolution for nation
and 10m or better in
some areas
Hillshade NED map for Rockville, MD
GIS 64
Physical features:U.S. Geological Survey
• Land cover
-Natural and
manmade
surface
features
-Collected from
satellites in
1992, 2001
GIS 65
Physical features: U.S. Geological
Survey
• National Map
Hydography Dataset
(NHD)
-Water bodies, lines,
and points
-Identifies segments
(reaches) with
network coding (flow
and direction)
GIS 66
ESRI’s Website
http://www.esri.com/data/resources/geographic-data.html
GIS 67
National Historic GIS
http://www.nhgis.org/
GIS 68
University websites
•Penn State’s PASDA
GIS 69
International sites
Rwanda Ministry of Health
GIS 70
International sites
USAID/PEPAR
GIS 71
State agencies
Texas Department of State Health
• http://www.dshs.state.tx.us/chs/
GIS 72
Local agencies
•Engineering Companies
-land surveys, aerial photos, CAD drawings
•Government agencies
-Adelaide Australia
Tip: search by “Adelaide Planning Department)
-Austin, TX
Tip: Search by county name (Travis, County Texas)
ftp://ftp.ci.austin.tx.us/GIS-Data/Regional/coa_gis.html
GIS 73
Local agencies
GIS 74