Download - Projections & Coordinate Systems
![Page 1: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/1.jpg)
Projections & Coordinate Systems
James PayneMorongo Band of Mission Indians
![Page 2: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/2.jpg)
Some definitions…
• Coordinates: at least 2 values that together define where a point is:– 12th Avenue and Main Street– 34.2942 N 116.2303 W
• Coordinate system: the rules that define how coordinates are placed and viewed– Where the “starting point” is– Provides values for measurements
![Page 3: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/3.jpg)
Some definitions…
• Projection: a method for displaying 2-dimensional maps (paper, monitor)– Dependent on area of interest and scale
• Datum: a framework or model for measuring locations on the earth– Different representations of the shape of the
earth provide different “views”
![Page 4: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/4.jpg)
Some details…
• A coordinate system uses a 3-dimensional sphere to define locations
• This is based off of a model (the datum)
![Page 5: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/5.jpg)
Some details…• The projection presents that 3-dimensional
information– All projections are based on a coordinate
system– Every map projection distorts distance, area,
shape, direction, or some combination thereof
• Imagine taking an orange, peeling it, and trying to flatten the peel – it will rip
![Page 7: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/7.jpg)
ConicPlanarCylindrical
Projections Visualized
Images from ESRI
![Page 8: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/8.jpg)
What does all this mean?
• You choose a coordinate system based on your data
• You choose a projection that will best represent your area of interest
Some examples….
![Page 9: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/9.jpg)
The points represent the same information, they are just shown in different views
![Page 10: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/10.jpg)
![Page 11: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/11.jpg)
Receiving data
• Find out the coordinate/projection• ArcMap will “reproject on-the-fly”, meaning
it knows how to display data in one coordinate system to look proper in another, but may present issues
• If receiving/providing coordinate data, need to know the datum to which it relates
![Page 12: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/12.jpg)
![Page 13: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/13.jpg)
These points have the same coordinate values, but are shown by differing coordinate systems (which are based off of different datums).
![Page 14: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/14.jpg)
What to use?• Look at where you will be obtaining data from
– What projection (with its associated coordinate system) is it in?
– Using the “predominant” one may increase productivity time but
• Are you happy with the display for your area?– If not, you can reproject it to fit your needs
• What do other users in your area use?
![Page 15: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/15.jpg)
• ArcMap automatically assumes the coordinate system of the map based off of the first layer added UNLESS it is previously set
• A common warning when adding data in a coordinate system that is different from the map
• Reproject on-the-fly
![Page 16: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/16.jpg)
Summary
• A coordinate system defines locations on earth
• A projection converts data from the round earth onto a flat plane
• Projections are designed for a specific purpose with different distortions
![Page 17: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/17.jpg)
Summary
• Most common datums used in North America are: – NAD 1927– NAD 1983– WGS 1984
• Know your data for proper display
• Use the metadata information
![Page 18: Projections & Coordinate Systems](https://reader036.vdocuments.net/reader036/viewer/2022062410/56816455550346895dd6226f/html5/thumbnails/18.jpg)
Questions, Comments?