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Spatial Data

What is Geographic Spatial Data?

What are its Properties

TWiST

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

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

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

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

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.

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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