1 spatial data what is geographic spatial data? what are its properties twist
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Spatial Data
What is Geographic Spatial Data?
What are its Properties
TWiST
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Where in the World…
• On the globe the coordinate system is Longitude (X) and Latitude (Y)
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North Pole
South Pole
Lat = 0º
Lat = -30º
Long = -60º
Lat = 30º
Lat = Zero Greenwich Goes 0 to 180 west and eastLong = zero at the Equator Goes 0 to 90 North and South
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Syracuse
-76.19 W 43.07N
How do we locate Syracuse on earth?
-76.19 degrees west of meridian through Greenwich, England
43.07 degrees N of the equator
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-76.19 degrees west of meridian through Greenwich, England
43.07 degrees N of the equator
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Can’t Xerox the Globe!• For a paper map have to convert
Long, Lat to some other coordinate system that will work on a flat surface.
• This conversion is called a “Projection”
• You can’t do a projection with out distortion of the globes surface features!
• For Example…5
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The world in Geographic Coordinates
IsAntarcticaReally that
big?
This is a Cartesian (rectilinear) Projection and shows a lot of distortion
Projection Not!
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Projections
• There are many Projection in use today (math example?)
• Some examples are…
MercatorAlbers
PolyconicLambert equal area Azimuthal
Peters
Albers equal area
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BUT, you don’t need to know that!
• Some of the spatial data you can get from the web is in Long, Lat.
• Use of that data causes problems• So most of the data you will see
will be in a Coordinate System– State Plane – different for each
state.– UTM (Universal Transverse Mercator)
• A common map is the USGS Quad Sheet…
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USGS 7.5 MIN QUAD MAPS
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• These maps have coordinates in their margins of• Long Lat• State Plane• UTM
• Available in:• Paper• Digital Image• Digital data layers
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Google Maps
• Google maps also have a coordinate system
• That’s how your navigator works!
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Spatial Data
• There are several types of spatial data– “Vector” types where all data is a
point, a line, or an area (polygon)– “Raster” Types where earth’s surface
is represented as a grid of cells • Elevation data• Image data
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PointsLines
Areas
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Raster Data
• Elevation Raster. Each cell has a value that is elevation
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UTM Zones
Most of NY is in UTM Zone 18
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UTM Coordinates
Easting
Northing
• The units in UTM are usually Meters
• You need to specify the zone
• Example: Location of Syracuse is ~: 406,534 Meters E, 4,766,472 Meters N, UTM Zone 18, N
O(~4,000,000) m in NY
O(~100,000) m in NY
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State Plane Zones
NY WestZone 4851
NY CentralZone 4826
NY EastZone 4801
NY Long IslandZone 4876
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DefinitionScale =
distance on map(distance unit)distance on ground (distance unit)
A Scale of 1/24,000 means
1 inch (or foot, or furlong) on the map =
24,000 inches (or feet or furlongs) on the ground.
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So?
• Why do you need to know this stuff?
• Because spatial data won’t overlay neatly if data is not in same spatial parameters
• BUT, most Geographic Information Systems will convert data if it is not in the same coordinate system as the First data layer added to a project.
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You do need to know some of this material
That is why we have provided you with a Spatial
Data Manual
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