1. Coordinate Systems & Vertical Datum Issues
Mark Seidelmann, PE, GISP
Erick Lobao, GISP
September 30, 2011
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Excited to be here
Partner could not be here
Originally intended for more general audience
Theme of the conference. You are here?
Practical example of a common problem
Not a surveyor

2. Introduction
Projections, datum's, and coordinate systems are an attempt to represent a 3 dimensional surface on a flat plane.
Real world significance (Floodplain Administrators).
Tips and Tricks.
Defining the Coordinate system and datum to be used early on avoids confusion later.
Definitions. Interchangeable jargon
Significance of projections
Live demo
Feedback-non esri users
Obvious take home- communicate and document
Intro – Definitions – Significance –Tools & Tricks– Conclusions

3. Definitions Map Projection:
A systematic representation of all or part of the surface of a round body on a plane.
Factors when picking a projection:
Area
Shape
Scale
Direction
Projections introduce Distortion.
Some preserve some features better than others.
Intro – Definitions – Significance – Tools & Tricks - Conclusions

4. Definitions Coordinate Systems:6 5
Coordinate Systems:
Reference System that uses numbers (coordinates) to define locations on a surface
Geographic:
Uses 3-d Surface
Latitude & Longitude
Length is variable
Projected:
Uses Flat Surface
X,Y
Length is constant
How you describe your location?
Two types of projections:
Geographic uses Latitude and Longitude (angles measured from the center of the earth).
Length is variable.
Projected: Assumes a flat surface. Uses X,Y coordinates.
Intro – Definitions – Significance – Tools & Tricks - Conclusions

5. Definitions Horizontal Datum: Where is origin (0,0)? Vertical Datum:6 5
Horizontal Datum:
Where is origin (0,0)?
Vertical Datum:
A reference surface from which elevation measurements are made.
Where is Elevation 0 ft? ?
In order to clearly share location information,
Compare different data sets.
You must know what origin your coordinate system references.
Datums link spheroid (model of the earth, to specific parts of the earths surface). The earth is not a sphere, varies, datums help account for this. ?
Intro – Definitions – Significance – Tools & Tricks - Conclusions

6. Common Coordinates in Ohio
Geographic:
World Geodetic System (WGS 84)
North American Datum 1983 (NAD83)
Projected:
State Plane – 2 zones North and South
NAD 27
NAD 83
NAD 83 HARN
UTM 16 and 17 north
Local Projections & Monuments
Projections for Different Purposes
Different data producers have different needs, and therefore use different coordinate systems.

7. Example (Floodplain Mapping)
Real world example of significance.
Flood insurance Rate maps are a “regulatory” tool.
Impact people.
Location & Elevation help determine where flooding occurs.
Datum shifts / impact coordinates and elevation values.

8. Datum Conversion It’s all Relative!
House Elev.
As maps get updated and Datums change, elevation values are impacted.
Everything moves together.
Can be difficult to communicate to home owners.
805
804 5
Flood Elev.
800
799
New Datum
Old Datum

9. Datum Conversion NADCON (NOAA) NGVD 29 Vs. NAVD 88
Vertical Datum Shift outlined in FEMA Guidelines and Specs Appendix B
Redelineated studies BFE’s haven’t changed
Datum shift is calculated for the county
Rarely shifted stream by stream
FEMA Reports specify & Document this.
NOAA - NADCON software to generate & measure this.
Use NADCON to Update legacy data

10. FIS and FIRM Data products impacted by datum changes.
Flood insurance Study (report)
Flood insurance Rate Map.

11. Issue 1: Different Projections
Issues
All my data is in NAD83 State Plane Ohio South
New data is in UTM 17N.
Solution
Make sure the new data is defined as UTM 17N.
Project the dataset to NAD83 State Plane South.
Common Mistake
Redefining data to NAD83 State Plane South.
Intro – Definitions – Significance – Tools & Tricks - Conclusions

12. Issue 2: Incorrect Projection
Issues
Projection on supplied data is incorrect or unknown.
Solution
Check Location.
Use data with known coordinates and compare.
Re-define Projection (start with the usual suspects).
Spatial adjustment tool
Common Mistake
Assuming the original projection was correct!
Intro – Definitions – Significance – Tools & Tricks - Conclusions

13. Ohio Identify the Coordinate System
State Plane South NAD83 or NAD27 Feet
(1,300,000 to 2,500,000 , 145,000 to 1,470,000)
State Plane South NAD83 meters
(400,000 to 770,000 , 44,500 to 450,000)
State Plane North NAD83 or NAD27 Feet
(1,300,000 to 2,500,000 , -460,000 to 850,000)
State Plane North NAD83 meters
(400,000 to 770,000 , -141,000 to 260,000)
UTM NAD83 17 N
(168,000 to 540,000, 4,250,000 to 4,650,000)
Geographic
( to , , )

14. Conclusions
Knowing the coordinate system and datum of your data is essential.
Unknown / wrongly defined coordinate systems can cause delays and mistakes.
Understand impacts of Datum Changes to your data.
Intro – Definitions – Significance – Tools & Tricks - Conclusions

15. Questions? Erick Lobao, Stantec, Project Manager, GISP
Mark Seidelmann, Stantec, Senior Project Engineer, PE, GISP
Intro – Definitions – Significance – Tools & Tricks - Conclusions