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

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) 2/25/2019 Louisiana's Spatial Domain

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 2/25/2019 Louisiana's Spatial Domain

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. 2/25/2019 Louisiana's Spatial Domain

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 2/25/2019 Louisiana's Spatial Domain

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. 2/25/2019 Louisiana's Spatial Domain

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 ... 2/25/2019 Louisiana's Spatial Domain

Example: Spatial Domain All GIS Features Must Fit Within this Positive, 32-bit Integer Space. OFF LIMITS 2,147,423,647 2,147,423,647 0 0 The Database’s Spatial Domain 2/25/2019 Louisiana's Spatial Domain

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. 2/25/2019 Louisiana's Spatial Domain

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. 2/25/2019 Louisiana's Spatial Domain

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 (123.456000) Multiply by Precision 123.456789 × 1000 Divide by Precision 123456 ÷ 1000 Integer Storage Unit in a Geodatabase (123456) X = 123.456789 Precision =1000 2/25/2019 Louisiana's Spatial Domain

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 2/25/2019 Louisiana's Spatial Domain

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. 2/25/2019 Louisiana's Spatial Domain

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. 2/25/2019 Louisiana's Spatial Domain

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. 2/25/2019 Louisiana's Spatial Domain

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 2.147 billion integer storage units. 2/25/2019 Louisiana's Spatial Domain

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? +30.3192129, -91.9826443 or +30.319, -91.983 2/25/2019 Louisiana's Spatial Domain

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 +/- 0.005 m 200 (five millimeters) 1000 (one millimeter) *The smallest value for precision is 1 2/25/2019 Louisiana's Spatial Domain

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.    2/25/2019 Louisiana's Spatial Domain

Louisiana's Spatial Domain Someone Else’s Job... Isn’t someone responsible for creating a standardized Spatial Domain and Coordinate Precision for Louisiana? YES... 2/25/2019 Louisiana's Spatial Domain

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 2/25/2019 Louisiana's Spatial Domain

Louisiana's Spatial Domain Max X = 1,137,595.909 Max Y = 3,773,695.909 Precision = 2287.000 or 1/2287 meters Min X = 198,600.000 Min Y = 2,834,700.000 2/25/2019 Louisiana's Spatial Domain

Louisiana's Spatial Domain Max X = 1,137,595.909 Max Y = 3,773,695.909 Precision = 2287.000 or 1/2287 meters Min X = 198,600.000 Min Y = 2,834,700.000 2/25/2019 Louisiana's Spatial Domain

Louisiana's Spatial Domain But wait, there’s more... Max X = 1,137,595.909 Max Y = 3,773,695.909 Z Domain = Range of Altitude Values (-500000 to 1647483.65 meters at 1/1000 meter precision) M Domains = Range of Linear Referenced Values (0 to 21474.84 meters at 1/100000 meter precision) Precision = 2287.000 or 1/2287 meters Min X = 198,600.000 Min Y = 2,834,700.000 2/25/2019 Louisiana's Spatial Domain

Don’t Let this Happen To You! Don’t Loose Data Because it Falls Outside the Domain! 2/25/2019 Louisiana's Spatial Domain

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 http://lagic.lsu.edu/mapserver 2/25/2019 Louisiana's Spatial Domain