Presentation on theme: "1 Spatial Data What is Geographic Spatial Data? What are its Properties TWiST."— Presentation transcript:
1 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) 22 North Pole South Pole Lat = 0º Lat = -30º Long = -60º Lat = 30º Lat = Zero Greenwich Goes 0 to 180 west and east Long = zero at the Equator Goes 0 to 90 North and South
3 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
4 -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
10 The world in Geographic Coordinates Is Antarctica Really that big? This is a Cartesian (rectilinear) Projection and shows a lot of distortion Projection Not!
11 Projections There are many Projection in use today (math example?) Some examples are… Mercator Albers Polyconic Lambert 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… 1212
USGS 7.5 MIN QUAD MAPS 13 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! 14
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 1515
20 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
21 State Plane Zones NY West Zone 4851 NY Central Zone 4826 NY East Zone 4801 NY Long Island Zone 4876
22 Definition Scale = 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. 23
You do need to know some of this material That is why we have provided you with a Spatial Data Manual 2424
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