Louisianas Spatial Domain or Everything youve ever wanted

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 Arc. GIS. • The Geodatabases is a relational database that stores geographic data. • Two Types of Geodatabases – Personal (for the desktop) – Enterprise (for an DBMS) 9/18/2020 Louisiana's Spatial Domain 2

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 9/18/2020 Louisiana's Spatial Domain 3

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. 9/18/2020 Louisiana's Spatial Domain 4

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). 9/18/2020 Geographic Coordinate System Projected Coordinate System Illustrates the 3 D shape of the Earth Illustrates a 3 D surface on a 2 D surface Louisiana's Spatial Domain 5

Storing Feature Coordinates Two Important Considerations when Storing Feature Coordinates in a Geodatabase: 1. All data is stored as positive, 32 -bit integers (i. e. Spatial Domain) 2. All data must maintain a Coordinate Precision. 9/18/2020 Louisiana's Spatial Domain 6

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. 14 x 109 meters, or miles, or inches, or arpents, or. . . 9/18/2020 Louisiana's Spatial Domain 7

Example: Spatial Domain • All GIS Features Must Fit Within this Positive, 32 -bit Integer Space. 2, 147, 423, 647 0 0 The Database’s Spatial Domain OFF LIMITS 9/18/2020 Louisiana's Spatial Domain 8

Storing Feature Coordinates Two important considerations when storing feature coordinates in a Geodatabase: 1. All data is stored as positive, 32 -bit integers (Spatial Domain) 2. All data must maintain a Coordinate Precision. 9/18/2020 Louisiana's Spatial Domain 9

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. 9/18/2020 Louisiana's Spatial Domain 10

Example: Coordinate Precision • Precision is a Scale Factor – Used to preserve decimal places before rounding – Larger precision preserves more digits X = 123. 456789 Precision =1000 Floating Point Coordinate in Arc. GIS (123. 456000) Multiply by Precision 123. 456789 × 1000 Divide by Precision 123456 ÷ 1000 Integer Storage Unit in a Geodatabase (123456) 9/18/2020 Louisiana's Spatial Domain 11

Example: Precision Preservation Coordinate System Units Storage Units = Precision Coordinate system units 9/18/2020 ÷ Precision = Storage units Meters 100 1 cm Meters 1000 1 mm Meters 50 2 cm Feet 12 1 inch Louisiana's Spatial Domain 12

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. 9/18/2020 Louisiana's Spatial Domain 13

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. 9/18/2020 Louisiana's Spatial Domain 14

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. 9/18/2020 Louisiana's Spatial Domain 15

The Zen Art of Geodatabase Design Become One with your Data! Learn how to modify your Spatial Domain: 1. Define your Coordinate Precision – Translate floating point coordinates into integer storage units 2. Define your Spatial Extents – Identify the maximum spatial extents for all your data without exceeding the 2. 147 billion integer storage units. 9/18/2020 Louisiana's Spatial Domain 16

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 9/18/2020 Louisiana's Spatial Domain 17

1. Calculating Precision Coordinate System Units Precision = Equipment Resolution (Desired Precision) Data collection method Coordinate system units Equipment resolution Minimum precision* Recommended precision Feet +/- 416 ft 1 (one foot) Professional GPS Meters +/- 0. 5 m 2 (half meter) 10 (one-tenth meter) Survey with theodolite Meters +/- 0. 005 m 200 (five millimeters) 1000 (one millimeter) Digitize 1: 250, 000 map *The smallest value for precision is 1 9/18/2020 Louisiana's Spatial Domain 18

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. 9/18/2020 Louisiana's Spatial Domain 19

Someone Else’s Job. . . Isn’t someone responsible for creating a standardized Spatial Domain and Coordinate Precision for Louisiana? YES. . . 9/18/2020 Louisiana's Spatial Domain 20

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. 4 mm precision 9/18/2020 Louisiana's Spatial Domain 21

Max X = 1, 137, 595. 909 Max Y = 3, 773, 695. 909 Precision = 9/18/2020 2287. 000 or 1/2287 meters Louisiana's Spatial Domain Min X = 198, 600. 000 Min Y = 2, 834, 700. 000 22

Max X = 1, 137, 595. 909 Max Y = 3, 773, 695. 909 Precision = 2287. 000 9/18/2020 or 1/2287 meters Louisiana's Spatial Domain Min X = 198, 600. 000 Min Y = 2, 834, 700. 000 23

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 9/18/2020 or 1/2287 meters Louisiana's Spatial Domain Min X = 198, 600. 000 Min Y = 2, 834, 700. 000 24

Don’t Let this Happen To You! Don’t Loose Data Because it Falls Outside the Domain! 9/18/2020 Louisiana's Spatial Domain 25

Get Your’s Today! TV AS SEE N O N • You too can have your very own copy of the Louisiana Spatial Domain http: //lagic. lsu. edu/mapserver 9/18/2020 Louisiana's Spatial Domain 26