Data Structures & GeoDatabase

GeoDatabase Implemented in a relational database Comes in two flavors – Personal & Enterprise (Access & Sys. Like Oracle) Supports a model of topologically integrated feature classes - 2D & 3D Supports Data Models -- ArcHydro Use can be simple or very complex! In some applications database designers will be needed to tune the database operation! Can use many different data structures

Outline Before looking at GeoDatabases we need to take a detailed look at the structure of the various types of data that can be used in a GeoDatabase Then we can look at the complexities of the GeoDatabase its self

Data Structures Images

Data Structures You have to know something about these Vector structures –Shapefiles (multiple files same name) –Coverages (Folders) Workstation – (folder with INFO file) PC (folder WITHOUT an INFO file) –Can only open in ArcView3.3 –Can then convert to a Shapefile

Data Structures You have to know something about these structures –Raster GRIDS –Images MrSid Tiff ERDAS Etc/

Vector: General Points are defined by a single x,y coordinate pair Lines are defined by two or more x,y coordinate pairs Polygons are defined by lines that close to form the polygon boundaries

3 Shape files for map Points, lines, polys

Vector: Shapefiles ExtensionRequiredWhat it is.dbf Attribute data file.shp Geometry.shx Index to geometry.sbn,.sbxSpatial index of features.fbn, fbxSpatial index read only features.ain, aihAttribute Index of active fields.xmlMetadata (AV8+).avlLegend data (Av3.x).prjProjection data etc.

Vector: Topology Shapefiles are said to have NO topology But they do (see Practical Vector GIS) WHAT IS IT??? Topological association: spatial relationship between features that share geometry In Coverages (Workstation & PC): spatial relationships between connecting or adjacent features in a data layer In GeoDatabases: a set of rules applied to feature classes that explicitly define spatial relationships that must exist between features.

Note: The chapter (2) in Practical Vector GIS has a lot of good information about this subject

Vector: Workstation Coverages Workstation ArcInfo coverages are a very common data structure They are stored in a workspace A Workspace is any folder that has –An INFO folder –And a set of coverages folders that have A bunch of.ADF files DON’T EVER MOVE THE CONTENTS OF A WORKSPACE EXCEPT IN ARC CATALOG!

Vector: Workstation Coverages Workstation ArcInfo coverages are a very common data structure A Workspace is any folder that has –An INFO folder –And a set of coverages folders that have A bunch of.ADF files These folders are all coverages Line data Extent Poly or Point Attribute Table TIC table An.AAT is a Arc Attribute table

A Coverage: points TIC

A Coverage: points

A Coverage: Arcs

2 Coverages for map Can’t have Points and Polys in same coverage because polys have a label point in each poly – confusion would abound!

Raster data We have looked at this structure before Here is ESRI’s diagram The elevation values are average for each cell in the raster There are a number of raster formats – ESRI’s is GRID

GRID STRUCTURE ESRI COURSE VIEW OF SOILS Explorer view A Workspace

Image data A raster-based representation of a scene Cell attributes are NOT like feature data Typically produced by an optical or electronic device, –camera or –scanning radiometer. Examples –remotely sensed data (for example, satellite data) –scanned data, and photographs. Stored as a raster dataset of binary or integer values that represent the intensity of reflected light, heat, sound, or any other range of values on the electromagnetic spectrum. An image may contain one or more bands.

Image data A raster-based representation of a scene Cell attributes are NOT like feature data Typically produced by an optical or electronic device, –camera or –scanning radiometer. Examples –remotely sensed data (for example, satellite data) –scanned data, and photographs. Stored as a raster dataset of binary or integer values that represent the intensity of reflected light, heat, sound, or any other range of values on the electromagnetic spectrum. An image may contain one or more bands..tif – tagged Image File Format.tfw – Tiff world file (location).sid – MrSID format (LizardTech).img – ERDAS Imagine format.jpg – Joint Photographic Experts …

USED FOR WHAT? Vector data – things with discrete borders –roads, minor civil divisions Raster data – continuous surfaces –Elevation, water table, sound levels Images – views of real world –Photos, satellite data

The Geodatabase It is a single container for many feature classes (FC) (layers, {themes} of any feature class type) Quite often the FCs are stored in Feature Datasets (FDS) Come in two flavors –Personal in Access databases –Enterprise in large commercial databases Oracle, DB2, SQL Server, ArcSDE

Geodatabase Feature Dataset Feature Classes Stand alone Feature Classes Source View

Display view ArcCatalog view } Cover Line (arc) point poly Anno Table

You need to consider... What will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tables What will be the projection & data extent used? What rules of data modification will be required? Do you want to maintain relationships between objects of different types? Will you be using geometric networks? Will you require topologically related features? Will you store custom objects?

Definitions Do all those words mean??????????

You need to consider... What will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tables What will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tables What will be the projection used? What rules of data modification will be required? Do you want to maintain relationships between objects of different types? Will you be using geometric networks? Will you require topologically related features? Will you store custom objects? Connectivity: Constraint on the type of network features that may be connected to one another –edge-junction rules –edge-edge rules Topology: Permissible relationships of features –within a feature class –between feature classes –between features in two different feature classes

You need to consider... What will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tables What will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tables What will be the projection used? What rules of data modification will be required? Do you want to maintain relationships between objects of different types? Will you be using geometric networks? Will you require topologically related features? Will you store custom objects? Associations or links between two or more objects in a GDB. Relationships can exist between 1) spatial objects (features in a feature class) 2) non-spatial objects (records in a table, or 3) spatial and non-spatial objects

You need to consider... What will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tables. What will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tables What will be the projection used? What rules of data modification will be required? Do you want to maintain relationships between objects of different types? Will you be using geometric networks? Will you require topologically related features? Will you store custom objects? Objects: The representation of a real world entity stored in a GDB. An object has properties and behaviors.

You need to consider... What will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tablesWhat will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tables What will be the projection used? What rules of data modification will be required? Do you want to maintain relationships between objects of different types? Will you be using geometric networks? Will you require topologically related features? Will you store custom objects? A one dimensional nonplaner graph (mathematics) that is composed of features. These features are constrained to exist within the network and can, therefor, be considered network features.

You need to consider... What will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tablesWhat will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tables What will be the projection used? What rules of data modification will be required? Do you want to maintain relationships between objects of different types? Will you be using geometric networks? Will you require topologically related features? Will you store custom objects? Relationships between connected features in a geometric network OR Shared borders between features in a topology (Now that is circular!!!!)

You need to consider... What will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tablesWhat will it be used for? What kind of data will be in the GDB –Themes and geometry types (point, line, poly?) –Attributes -- spatial or non-spatial tables What will be the projection used? What rules of data modification will be required? Do you want to maintain relationships between objects of different types? Will you be using geometric networks? Will you require topologically related features? Will you store custom objects? Custom Objects: In ArcGIS you are NOT limited to the objects provided. New objects can be added

More Definitions: Feature An object class in a GDB that has a field of type GEOMETRY. –Are stored in Feature Classes A representation of a real world object A point, line or poly in a coverage or shapefile A representation of a real world object in a layer on a map.

More yet: Feature Class Conceptual representation of a category of geographic features. Includes point, line, poly & annotation In a GDB, an object that stores features and has a geometry field type

Feature Dataset A collection of feature classes that share the same spatial reference. It is because they share the same spatial reference that they can participate in topological relationships with each other. Several feature classes with the same geometry may be stored in the same feature dataset. Object geometry and relationship classes can also be stored in a feature dataset

Some others Edge: –A line segment in a topology that defines lines or polys boundaries –Multiple features in one or more feature classes may share topology edges Dataset: –Any feature class, table, or collection of feature classes or tables in the GDB –A named collection of logically related data items arranged in a prescribed manor

Icons GDB Feature Dataset GDB table

Icons GDB Feature Dataset GDB table

Icons GDB Feature Dataset GDB table

Three ways to create a GDB Plan it Import Existing Data Create a Schema with ArcCatalog Use CASE tools Define connectivity rules, relationships Load data into Schema: Shapefiles Coverages GDB

Feature Datasets (FDS) Exist in a GDB to define a particular Spatial Reference Are a way to group feature Classes(FC) with the same spatial reference So they can participate in topological relationships with each other Topologically related FCs must reside in the same FDS

Spatial Reference A coordinate System –Geographic –UTM –Etc. A spatial domain (coord range, measures (M), and Z values (extent) Precision (# of system units/unit M) MUST be specified when creating a FDS and it feature classes or a stand alone feature class

Field Properties When creating a Feature Class or table you can specify the number of fields to be included And you can spec settings such as field type and max. size All fields have property default values, domains, aliases, and null allowance

Field Properties When creating a Feature Class or table you can specify the number of fields to be included And you can spec settings such as field type and max. size All fields have property default values, domains, aliases, and null allowance Set values at creation time Valid set or range of values for the field Aliases will display on maps Yes or NO for allowing nulls (nothing)

Field Precision & Scale Max. field size and precision –Precision – number of digits (not the “.”) –Scale – number of decimal places Personal GDBs support ONLY binary fields and precision and scale are ignored! NOT SO for enterprise GDB!!!

Required Fields Apply to all feature classes and tables Automatically created Required fields also have required properties (domain) [can’t change] Required fields for simple FCs are –OBJECTID –Shape Note: when you import data there will be other fields you cannot change in ArcGIS – But you can change them in ACCESS

Topologies Many datasets have features that could share boundaries or corners By creating a Topology you set up rules defining how features share their geometries. Editing a boundary or vertex shared by two or more features updates the shape of all of them.

Topology rules Govern the relationships between between features within a FC or features in different FCs Example: moving a slope boundary in in one FC could update two slope class polys AND update a forest stand boundary in another FC. Topology editing tools in ArcMap are used to create and change the rules

Geometric Networks Some vector datasets need to support connectivity tracing and network connectivity rules –Communications –Pipelines –Transportation (roads, railroads, canals) Geometric networks allow you to turn simple point and line features into network edge and junction features

Data Numeric data can be stored in 4 types –Short integer –Long integer –Single precision floating point (floats) –Double precision floating point (doubles)

Decimal vs. Binary Important concept 8,4,2,1 place weight The binary number 0110 = 6 in decimal 0001 = 1, 0010 =2, 0011 = 3, 0100 =4 The short integer is 16 bits or 2 bytes One is for sign leaving 15 for the number Range is –32,000 to +32,000 The long integer is 4 bytes or 32 bits Range is –2 billion to +2 billion (more or less)

Decimal vs. Binary Floats and doubles are coded in a form similar to scientific notation -3,125  x 10 3  3.125E 3 Float is a 8 bit number and store up to 7 significant digits – -3.4E -38 to –1.2E 38 for neg numbers – 3.4E -38 to 1.2E 38 for positive As a result floats and doubles are only approximate numbers!!!!!!!!

More yet You cannot express the number 1,234,567.8 as a float because it contains more than 7 digits. As a float it will be 1,234, cannot be expressed exactly -- it will be

Summary of data types NameRange, length Size (bytes) Applications Short Integer -32,768 to 32,767 2No fractions Long Integer -2,147,483,648 To 2,147,483,647 4No fractions Float~-34E -38 to ~1.2E 38 4Fractional values

Summary of data types NameRange, length Size (bytes) Applications Double~ -2.2E -308 ~ 1.8E 308 8Fractions OK Text <=64,000 char varies Names etc. Date mm/dd/yy hh:mm:ss 8Date and time

The BLOB Binary Large Object Simply some data stored in the GDB as a long sequence of binary numbers. Such as –Images –Multimedia –Code

Summary GDB Feature Datasets Feature Classes Features