1. LA GIS Council Presentation January 20, 2005
Louisiana’s Spatial Domain or Everything you’ve ever wanted to know about Geospatial Domains & Coordinate Precision, but were afraid to ask.
Dr. Jim Mitchell, DOTD
Joshua Kent, LAGIC
LA GIS Council Presentation January 20, 2005

2. Louisiana's Spatial Domain
The Geodatabase
The Geodatabase is a data format used within ESRI’s ArcGIS.
The Geodatabases is a relational database that stores geographic data.
Two Types of Geodatabases
Personal (for the desktop)
Enterprise (for an DBMS)
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3. Geodatabase Structure
A Container for Managing GIS Data Objects
Features (shape, line, polygon)
Feature Datasets (topologically related feature classes)
Non-spatial Tables (attribute data)
All Feature Objects are Spatially Referenced
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4. Spatially Referenced Data
We use a Reference System to determine the location of features on Earth or on a map.
In a GIS, the reference systems used to determine feature locations are called Coordinate Systems.
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5. Coordinate Systems Two Types of Coordinate Systems:
GEOGRAPHIC: used to locate objects on the curved surface.
PROJECTED: used to locate objects on a flat surface (i.e. paper, computer screen).
Geographic Coordinate System
Illustrates the 3D shape of the Earth
Projected Coordinate System
Illustrates a 3D surface on a 2D surface
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6. Storing Feature Coordinates
Two Important Considerations when Storing
Feature Coordinates in a Geodatabase:
All data is stored as positive, 32-bit integers (i.e. Spatial Domain)
All data must maintain a Coordinate Precision.
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7. Louisiana's Spatial Domain
1. The Spatial Domain
The Geodatabase stores all geometry coordinates as positive integers
Faster Display, Processing, and Analysis
Better Compression (DBMS only)
Efficient for managing topologic relationships
Limited to 2,147,423,647 storage units.
2.14x109 meters, or miles, or inches, or arpents, or ...
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8. Example: Spatial Domain
All GIS Features Must Fit Within this Positive, 32-bit Integer Space.
OFF LIMITS
2,147,423, ,147,423,647
0 0
The Database’s Spatial Domain
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9. Storing Feature Coordinates
Two important considerations when storing
feature coordinates in a Geodatabase:
All data is stored as positive, 32-bit integers (Spatial Domain)
All data must maintain a Coordinate Precision.
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10. Louisiana's Spatial Domain
2. Coordinate Precision
The geodatabase converts all coordinates into 32-bit Storage Units.
Storage Units are the smallest measurable unit that can be stored in a Geodatabase.
Precision is used to convert coordinate system units into storage units.
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11. Example: Coordinate Precision
Precision is a Scale Factor
Used to preserve decimal places before rounding
Larger precision preserves more digits
Floating Point Coordinate in ArcGIS
( )
Multiply by Precision × 1000
Divide by Precision ÷ 1000
Integer Storage Unit in a Geodatabase (123456)
X = Precision =1000
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12. Example: Precision Preservation
Coordinate System Units Precision
Storage Units =
Coordinate system units ÷
Precision =
Storage units
Meters
100
1 cm
1000
1 mm 50
2 cm
Feet 12
1 inch
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13. Louisiana's Spatial Domain
Don’t Look... It’s Magic!
Spatial Domain and Precision Values Will Be Set Automatically:
Spatial Domain and Precision will be defined by the first feature class imported.
Automatic Settings Are Bad
Errors can occur when importing features into a Feature Dataset.
Values must be set deliberately to guarantee a specific precision.
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14. Why is this so important?
Data Management
Larger Domains will support larger geographic areas.
Larger Domains are maintained at the expense of precision.
Topology
Topology defines the relationship one feature class has with another.
Topology = Efficient Data Management
Example: Modifying the border of one feature class simultaneously modifies the borders of other feature classes.
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15. Why else is this important?
Data Sharing
A standardized Spatial Domain & Coordinate Precision ensures that all features can be shared by all parties without impacting accuracy.
Understanding your Data
Understanding the relationship your data shares with its environment.
Understanding the level of precision at which your data was collected/created.
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16. The Zen Art of Geodatabase Design
Become One with your Data!
Learn how to modify your Spatial Domain:
Define your Coordinate Precision
Translate floating point coordinates into integer storage units
Define your Spatial Extents
Identify the maximum spatial extents for all your data without exceeding the billion integer storage units.
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17. 1. Calculating Precision
Store Precision Based on Data Quality
Match storage units to equipment resolution
Not all floating-point digits will represent actual data
How Precise is your GPS?
, or ,
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18. 1. Calculating Precision
Coordinate System Units Equipment Resolution (Desired Precision)
Precision =
Data collection method
Coordinate system units
Equipment resolution
Minimum precision*
Recommended precision
Digitize 1:250,000 map
Feet
+/- 416 ft
1 (one foot)
Professional GPS
Meters
+/- 0.5 m
(half meter)
10 (one-tenth meter)
Survey with theodolite
+/ m
200
(five millimeters)
1000 (one millimeter)
*The smallest value for precision is 1
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19. 2. Define the Spatial Domain
Spatial Domain = Max Spatial Extents
Cannot exceed 2,147,483,647 storage units (or 231-1)
Cannot change once it’s been defined.
  
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20. Louisiana's Spatial Domain
Someone Else’s Job...
Isn’t someone responsible for creating a standardized Spatial Domain and Coordinate Precision for Louisiana?
YES...
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21. Louisiana’s Spatial Domain
Developed For the LA GIS Council
Encompasses Louisiana and Surrounding Areas
Maintains High Level of Precision (.0004 meters)
Characteristics:
UTM Coordinate System, Zone 15
North American Datum 1983
Meter Units
0.4mm precision
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22. Louisiana's Spatial Domain
Max X = 1,137, Max Y = 3,773,
Precision = or 1/2287 meters
Min X = 198, Min Y = 2,834,
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Louisiana's Spatial Domain

23. Louisiana's Spatial Domain
Max X = 1,137, Max Y = 3,773,
Precision = or 1/2287 meters
Min X = 198, Min Y = 2,834,
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Louisiana's Spatial Domain

24. Louisiana's Spatial Domain
But wait, there’s more...
Max X = 1,137, Max Y = 3,773,
Z Domain = Range of Altitude Values ( to meters at 1/1000 meter precision)
M Domains = Range of Linear Referenced Values (0 to meters at 1/ meter precision)
Precision = or 1/2287 meters
Min X = 198, Min Y = 2,834,
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25. Don’t Let this Happen To You!
Don’t Loose Data Because it Falls Outside the Domain!
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Louisiana's Spatial Domain

26. Louisiana's Spatial Domain
Get Your’s Today!
AS SEEN ON TV
You too can have your very own copy of the Louisiana Spatial Domain
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Louisiana's Spatial Domain