Organizing Geographic Data Learning ArcGIS Desktop Training Course

Organizing Geographic Data Learning ArcGIS Desktop Training Course
Module 4 ESRI Virtual Campus Learning ArcGIS Desktop Training Course ESRI ArcGIS Section 1

Introduction First step in creating geographic data Geographic data
Identifying features, events, and phenomena and associating them with a location Geographic data recorded information about the earth's surface and the objects found on it, associated to a geographic location. In this module, you will learn more about geographic data—how it is organized and stored in a GIS, and how it can be assembled into a useful GIS database. Section 1

Learning Objectives Describe two common data models used to represent geographic data List different geographic data formats Determine the data source of a layer in ArcMap Identify data formats in ArcCatalog Create a geodatabase Add data from different formats to a geodatabase Section 1

Exploring Geographic Data
Before working with data in a GIS Data must be in a digital format How to translate real-world features into digital features? Data model Defines how to abstract real-world features into a format that can be understood by a computer. Two main data models used to represent features Section 1

Geographic Data Models
Two common data models used to represent geographic data Vector data model Raster data model Section 1

Vector Data Model Based on assumption earth's surface composed of discrete objects Trees, rivers, lakes, etc. Objects represented as point, line, and polygon features with well-defined boundaries Feature boundaries are defined by x,y coordinate pairs which reference location in real world Section 1

X, Y Coordinates Pair of values that represents On a map
distance from an origin (0,0) along two axes horizontal axis (x) representing east-west vertical axis (y) representing north-south On a map x,y coordinates represent features at location found on earth's spherical surface Section 1

Vector Data Model Points Lines Polygons
Defined by single x,y coordinate pair Lines Defined by two or more x,y coordinate pairs Polygons Defined by lines that close to form the polygon boundaries Section 1

Vector Data Model Every feature is assigned a unique numerical identifier Stored with feature record in attribute table Section 1

Raster Data Model Earth is represented as grid of equally sized cells.
An individual cell represents a portion of the earth such as a square meter or a square mile Only one x,y coordinate pair is normally present Called the origin Used to define the location of every cell Each cell's location is defined in relation to the origin Section 1

Raster Data Model Each raster cell is assigned a numeric value
can represent any kind of information about that geographic location Elevation measurement in meters Code number that specifies type of vegetation Section 1

Raster Data Model Represents geographic data
Elevation Rows and columns of equally sized cells One corner must be defined by x,y coordinate pair Section 1

Which Data Model? Vector data model Raster data model
To represent features that have discrete boundaries A building Polygon feature x,y coordinates recorded for its corners More accurate Raster data model To represent discrete features as well. A building Group of connected cells with same value Code value for building. Less storage space Section 1

Which Data Model? Vector data model Raster data model
represents geographic features with exactly defined boundaries Raster data model represents them as cells of the same value Shapes of the raster building and road don't seem as similar to the real-world shapes Section 1

Which Data Model? Raster data model
Very useful for representing continuous geographic data Don't have well-defined boundaries Usually change gradually across a given area i.e. elevation, precipitation, and temperature When used to represent continuous data each cell value is a measure of the phenomenon being modeled An elevation raster each cell value represents the elevation of a particular area. Commonly used for spatial analysis and modeling Section 1

Organizing Vector Data
Feature Basic unit of vector data Feature class Basic storage unit for features A collection of features that Share same geometry type and same attributes Located within common geographic extent Examples All customer locations for group of business franchises = point feature class named "Customers" All roads in a city =line feature class named "Roads" Areas in a city =polygon feature class called "Zoning" Section 1

All features in a feature class have the Same geometry type Same attributes Are located within a common geographic extent Section 1

Three common data formats that use feature classes Geodatabase Coverage Shapefile Section 1

Geodatabase Data storage format introduced with ArcGIS® software
Relational database Composed of various tables that organize data and are linked to one another Think of a geodatabase as A container for storing geographic data. Geographic data stored in a geodatabase may be Collection of vector feature classes Point, line, polygon, or annotation Raster datasets Tables Section 1

Geodatabase Basic components are
Tables Feature classes Raster datasets Has many powerful capabilities for modeling real-world objects Section 1

How a Geodatabase Organizes Data
Feature classes can be Stand-alone Organized into components called feature datasets Feature dataset stores feature classes that have the same coordinate system Not all features have to have the same geometry type Can store feature classes with different geometry types i.e. a feature dataset representing sewers may store a line feature class representing mains a point feature class representing valves Section 1

Feature classes grouped into a feature dataset Normally have spatial relationships to one another i.e. might be adjacent, intersect, or coincide with each other Feature class tables Store feature geometry and attribute information Section 1

Some attributes are automatically created and maintained by the geodatabase Line feature classes Calculates length of each feature and stores data in a field called Shape_Length Polygon feature classes Calculates perimeter and area of each feature and stores in fields called Shape_Length and Shape_Area Section 1

Nonspatial tables Geodatabase tables that contain only feature attributes—no geometry Feature attributes stored outside feature class table in separate table Used for database efficiency To speed up data queries and feature draw time Section 1

A geodatabase can contain Stand-alone feature classes Feature classes grouped into feature datasets Raster datasets Nonspatial tables Section 1

Coverages File-based data format native to ESRI's ArcInfo® Workstation software Conceptually, coverages can be thought of as a combination of other vector data formats you have learned about. Like a feature class, coverages have a geometry type of point, line, or polygon. And, also like a feature class, a coverage represents a single thematic layer, such as schools, streets, or land use, in which all features have the same attributes and are located within a common geographic area. On the other hand, coverages are like a geodatabase feature dataset because they store a set of spatially related feature classes. Point, line, and polygon coverages each contain a different set of feature classes that, together, define their features. Section 1

Coverages Geometry type of the coverage
determines which feature classes it will store Section 1

Main Coverage Feature Classes
Point feature class stores the point features of a point coverage Arc feature class stores the line features of a line coverage or the polygon boundaries of a polygon coverage Polygon feature class Stores polygon features of a polygon coverage Label feature class Stores points in center of each polygon of a polygon coverage Used to place feature labels Tic feature class Stores geographic control points that represent known real-world coordinates Used to reference coverage features to the real world All coverages have a tic feature class Section 1

More About Coverages Coverages can contain many more types of feature classes Annotation Routes Regions For more information refer to the ArcGIS Desktop Help (Contents tab -> Data support in ArcGIS -> Coverages) Section 1

Coverages Attributes and spatial relationships associated with a coverage feature class stored in INFO-format tables INFO tables stored in a folder called info which is stored with the other coverage files in a workspace folder. Even if there is more than one coverage in a workspace folder, there is always only one info folder that contains the INFO tables for all the coverages in that workspace. Section 1

Coverages How coverages are displayed in Windows Explorer.
Coverages workspace folder contains 3 coverages: Landuse Schools Streets The info folder contains the INFO tables associated with each of those coverages Section 1

Coverages Always use ArcCatalog to manage coverages
Won't see the info folder associated with a coverage in the ArcCatalog™ Catalog Can see it in your operating system's file manager (e.g., Windows Explorer) Never move, copy, rename, or delete a coverage using your operating system's file manager Connection between coverage feature classes and info folder could become broken or corrupted Section 1

Shapefiles File-based data format
native to ArcView® 3.x software A shapefile is composed of at least 3 files, and as many as 8 Each file has shapefile name and extension .shp, .shx, .dbf Information stored allows features and attribute table to be displayed Section 1

Shapefile Files ShapefileName.dbf ShapefileName.shp ShapefileName.shx
dBASE-format table that stores feature attributes ShapefileName.shp stores feature geometry ShapefileName.shx stores the index of the feature geometry Section 1

Additional Shapefile Extensions
ShapefileName.aih attribute index file ShapefileName.ain ShapefileName.prj coordinate system file ShapefileName.sbn spatial index file ShapefileName.sbx Section 1

Shapefiles In ArcCatalog
Can only see.shp extension Can view all shapefile files in Windows Explorer Always use ArcCatalog to manage shapefiles ArcCatalog accesses all shapefile files when renaming, moving, copying, or deleting Section 1

Shapefiles Files associated with a shapefile are visible in Windows Explorer Named CensusBlocks Section 1

Shapefiles Common data format ArcPad® software
Global positioning system (GPS) applications Section 1

Raster Data Formats Two common data formats based on the raster data model are Grids Images Section 1

Grids Used to store both Cells Two types of grids discrete features
buildings, roads, and parcels continuous phenomena elevation, temperature, and precipitation Cells Basic unit of raster data model Store information about what things are like at a particular location on the earth's surface. Depending on type of data being stored values can be either integers (whole numbers) floating points (numbers with decimals). Two types of grids one stores integers One stores floating points Section 1

Discrete Grids Contains cells whose values are integers
Often code numbers for a particular category Cells can have the same value i.e. land use each land use type is coded by a different integer But many cells may have the same code. Have an attribute table that stores cell values and their associated attributes Section 1

Continuous Grids Continuous grid
Used to represent continuous phenomena Cell values are floating points Each cell can have a different floating point value i.e. elevation one cell might store an elevation value of meters while the cell to the left might store an elevation value of meters don't have an attribute table Section 1

Grids Discrete grids represent discrete features such as land use categories with integer values Continuous grids represent continuous phenomena such as elevation with floating point values Section 1

Grids Attribute tables of discrete grids INFO format
same format as coverage feature class attribute tables Stored within an info folder which is stored at the same level as the grid in a workspace folder One info folder for all the grids in a workspace folder To avoid breaking or corrupting the connection between grid files and the info folder, always use ArcCatalog to move, copy, rename, and delete grids Section 1

Grids Grids workspace folder contains 2 grids
Soils Vegetation Attribute tables for both grids stored in info folder Auxiliary files link grids and attribute tables soils.aux vegetation.aux Section 1

Images Collective term for rasters whose pixels Commonly used in GIS
store brightness values of reflected visible light or other types of electromagnetic radiation emitted heat (infrared) ultraviolet (UV) Commonly used in GIS Aerial photos satellite images scanned paper maps Section 1

Images Can be displayed as To be displayed as a layer Layers in a map
Attributes for vector features i.e. a real estate company might include photos of available houses as an attribute of a homes layer To be displayed as a layer Must be referenced to real-world locations i.e. an aerial photo as it comes from the camera just a static picture no geographic information photo may contain distortion and scale variations To display properly with other map layers photo must be assigned a coordinate system some of its pixels must be linked to known geographic coordinates Section 1

Images Raster images i.e. aerial photographs and scanned maps
can be referenced to real-world locations then displayed as a layer in a GIS map Section 1

Image File Formats Differ in the type of compression used to reduce the file size Some supported by ArcGIS software .tif (Tagged Image File Format) .sid (LizardTech MrSID) .img (ERDAS Imagine) .jpg (Joint Photographic Experts Group) Section 1

Exercise Explore Geographic Data Section 1

Organizing Data into a Geodatabase
Geographic data can be stored in a variety of formats. To assemble geographic data into a GIS database create a collection of folders containing data stored in different formats i.e. shapefiles and coverages Or create a geodatabase Section 1

Advantages of Geodatabase
All data is stored in one central location Helps maintain an overview of data holdings and more easily locate data Promotes faster and more accurate data entry and editing Can set up rules for a geodatabase feature class that say only certain values are valid for a particular attribute, and create relationships among feature classes so that when a feature in one feature class is updated, related features in other feature classes update Section 1

Advantages of Geodatabase
Automatically calculates and maintains geometric values for Line and polygon feature classes Length, perimeter, and area Extremely valuable if doing analyses that rely on these measures Section 1

Types of Geodatabases File geodatabases
Personal geodatabases for Microsoft® Access™ ArcSDE geodatabases Section 1

Types of Geodatabases Type depends on
what data will be used for Structure and workflows of the organization Small workgroup, and data edited by single user File geodatabase most suitable File geodatabase can handle very large datasets with very fast performance Storage capacity virtually unlimited Requires less disk space than other file formats Recommended data format for ArcGIS Personal geodatabase for Access also designed for small workgroups with single editor Uses Microsoft Access data format with the .mdb file extension Section 1

Types of Geodatabases Large organization – i.e. a city government
Geodatabase may store inventory of all data available for administration of the city. Different departments will use data and multiple people will need to access and edit the data at the same time. In this case ArcSDE geodatabase is probably the best choice. ArcSDE geodatabases Can support increasing numbers of concurrent users and editors Require a relational database management system such as DB2, Oracle, or SQL Server and ESRI's ArcSDE® technology Section 1

Types of Geodatabases File geodatabases, personal geodatabases for Access, and ArcSDE geodatabases store the same basic elements feature classes (stand-alone or in feature datasets) raster datasets nonspatial tables Section 1

Designing a Geodatabase
Before looking for data Must know what data to look for Requires some thinking, planning and design Before building a geodatabase Identify all data it will store and decide on best way to structure that data Asking the right questions in the beginning may help avoid some pitfalls that can cost time and money Strive to organize geographic data to best serve the needs of the organization Section 1

Questions to Ask Before Building a Geodatabase
What will the geodatabase be used for? Listing possible application scenarios will help identify thematic data layers needed to store i.e. suppose you will be evaluating fire hydrant coverage in a particular part of town. You might decide that you need to store fire hydrants and streets as well as buildings and parcels in the geodatabase What data layers do you need? After identifying possible applications, there will be a good understanding of what datasets will be needed List them out What attributes do you need? Information from a GIS is only as good as the information put in i.e. For the fire hydrant coverage project, you might need attributes such as hydrant IDs, street names, building addresses, parcel IDs, parcel owners, and parcel owner addresses Section 1

Questions to Ask Before Building a Geodatabase
At what level of detail should features be represented? Decide on geometry type of each data layer. Will fire hydrants be represented as points or polygons? Will streets be represented as lines or polygons? When making these decisions, consider how accurately (with how much detail) you need to represent features in order to perform the tasks for all the possible applications. How should attributes be stored? Attributes can be stored along with associated features in a feature class table Nonspatial tables can be created to store attributes i.e. Building addresses should probably be stored with the buildings feature class since they are not likely to change, but the parcel owner addresses could either be stored in the parcels feature class or in a separate nonspatial table. Storing attributes outside the feature class may make sense when they change often. Which feature classes are spatially related? If certain feature classes are spatially related, group them into a feature dataset Store buildings and parcels in a feature dataset because the two feature classes are spatially related buildings are always contained within a parcel Section 1

Result of design work  plan or model of the geodatabase Design model best illustrated in a diagram that shows Feature classes Feature datasets Nonspatial tables A list of feature attributes Section 1

Diagram shows structure of planned geodatabase Will contain One feature dataset Two stand-alone feature classes A nonspatial table Section 1

Data Resources Common problem doing GIS  finding needed data
Often, when starting a GIS project, you will have some, but not all, the data required for the project. List of Data Marts ESRI Geography Network Geospatial One-Stop National Atlas of the United States National Park Service NOAA National Geophysical Data Center U.S. Geological Survey (USGS) EROS Data Center National Map Seamless Data Distribution Sys Section 1

Data Resources State data clearinghouses Commercial data vendors
Alaska California Hawaii Commercial data vendors GIS Data Depot GIS Lounge Map Mart Section 1

Getting Data into a Geodatabase
Once you have a design for your geodatabase, you can add data to it. There are three ways to get data into a geodatabase: Import data Load data Copy data Section 1

Importing Data Data can be imported into geodatabase feature classes and tables Create feature classes or tables and populate them with data at the same time Can import multiple data files at once Can exclude attributes from being imported By default  spatial reference of data imported into the geodatabase = same spatial reference as source files Section 1

Loading Data Loading Creating new, empty feature classes, feature datasets, and nonspatial tables, then populating them with data Data from multiple source files can be loaded and combined into one geodatabase feature class Can also select which features and attributes loaded Can populate empty feature classes and tables by creating new data in ArcMap When loading existing data into empty feature classes spatial reference and the name, type, and length of the attribute fields in the source files and in the empty feature class must be the same If some attribute fields in new feature class don't match ones in source files, only matching attributes will be loaded Section 1

Copying Data Can copy and paste if data exists in another geodatabase
When copying and pasting feature classes into a feature dataset Make sure spatial reference of both feature datasets are the same Section 1

Understanding Field Types
When creating new, empty feature classes and tables Important to be aware that the field type of an attribute determines what data can be stored in it. Section 1

Understanding Field Types
Stored Values Application Short integer Numbers from -32,768 to 32,768 Numeric values without decimal places Long integer Numbers from -2,147,483,648 to 2,147,483,648 Large numeric values without decimal places Float Approx * E-38 to 1.2 E38 Numeric values with or without decimal places Double Approx. -2.2*E-308 to 1.8* E308 Large numeric values with or without decimal places Text Up to 64,000 characters Text strings such as names and descriptions Date Mm/dd/yyyy hh:mm:ss AM/PM Date and time values Blob (binary large object) Varies Images and other multimedia GUID 36-character string enclosed in curly brackets Unique feature IDs within and across geodatabases Raster Raster data Raster datasets as attributes Section 1

Exercise Create a project database Section 1

Review Geographic data
recorded information about earth's surface and objects found on it associated to a geographic location Two models for representing real-world features in a GIS Vector data model Raster data model Common file formats for storing vector data Geodatabases Shapefiles Coverages Common file formats for storing raster data Images Grids Section 1

Review Three types of geodatabases Geodatabase feature classes can be
File geodatabases Personal geodatabases for Microsoft Access ArcSDE geodatabases Used with relational database management systems and ArcSDE technology Geodatabase feature classes can be Stand-alone Feature datasets organized into larger units Field type of an attribute determines type of data that can be stored in it Section 1

Review Questions When would you use the vector data model versus the raster data model? In a geodatabase polygon feature class, which two fields are automatically calculated and updated? List three methods of adding data to a geodatabase. If you wanted to combine features from different feature classes into one feature class, which method would you use? Section 1

Review Answers If you want to represent features with distinct boundaries, it's probably better to use the vector data model and store the features' x,y coordinate locations. The raster data model is better suited to representing phenomena whose boundaries change gradually across a given area. In a geodatabase polygon feature class, the Shape_Length and Shape_Area fields are automatically calculated and updated. Three methods of adding data to a geodatabase are importing, loading, and copying data. To combine features from different feature classes into one feature class, you would load them into a new, empty geodatabase feature class. Section 1

Key Terms Coverage Data model Feature class
A data model for storing geographic features using ArcInfo software. A coverage stores a set of thematically associated data considered to be a unit. It usually represents a single layer, such as soils, streams, roads, or land use. In a coverage, features are stored as both primary features (points, arcs, polygons) and secondary features (tics, links, annotation). Feature attributes are described and stored independently in feature attribute tables. Coverages cannot be edited in ArcGIS. Data model In a general sense, an abstraction of the real world which incorporates only those properties thought to be relevant to the application at hand. It would normally define specific groups of entities, their attribute values, and the relationships between these. In GIS, it is often used to refer to the mechanistic representation and organization of spatial data; for example, the vector data model and the raster data model. A data model is independent of a computer system and its associated data structures. Feature class A collection of geographic features with the same geometry type (such as point, line, or polygon), the same attributes, and the same spatial reference. Feature classes can stand alone within a geodatabase or be contained within shapefiles, coverages, or other feature datasets. Feature classes allow homogeneous features to be grouped into a single unit for data storage purposes. For example, highways, primary roads, and secondary roads can be grouped into a line feature class named "roads." In a geodatabase, feature classes can also store annotation and dimensions. Section 1

Key Terms Feature dataset Geodatabase Grid
In a geodatabase, a collection of feature classes stored together that share the same spatial reference; that is, they have the same coordinate system and their features fall within a common geographic area. Feature classes with different geometry types may be stored in a feature dataset. Geodatabase A relational database that stores geographic data. More precisely, the geodatabase is an object-oriented data model introduced by ESRI that is used to store spatial and attribute data and the relationships that exist among them. The geodatabase provides tools for creating "smart" geographic features and enforcing database integrity. A geodatabase can store feature classes, feature datasets, nonspatial tables, and relationship classes. Grid A raster data format that defines geographic space as an array of equally sized cells arranged in rows and columns. Each cell stores a numeric value that represents a geographic attribute (such as elevation) for that unit of space. When the grid is drawn as a map, cells are assigned colors according to their numeric values. Each grid cell is referenced by its x,y coordinate locations. In cartography, any network of parallel and perpendicular lines superimposed on a map and used for reference. Grids are usually named after the map's projection; for example, Lambert grid and Transverse Mercator grid. Section 1

Key Terms Image Raster Shapefile
A raster-based representation or description of a scene, typically produced by an optical or electronic device such as a camera or a scanning radiometer. Common examples include remotely sensed data (for example, satellite data), scanned data, and photographs. An image is 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. Raster A spatial data model that defines space as an array of equally sized cells arranged in rows and columns. Each cell contains an attribute value and location coordinates. Unlike a vector structure, which stores coordinates explicitly, raster coordinates are contained in the ordering of the matrix. Groups of cells that share the same value represent geographic features Shapefile A vector data storage format for storing the location, shape, and attributes of geographic features. A shapefile is stored in a set of related files and contains one feature class. Section 1

Key Terms Thumbnail Vector x,y coordinates
A snapshot describing the geographic data contained in a data source, layer, or map. A thumbnail might provide an overview of all the features in a feature class or a detailed view of the features in, and the symbology of, a layer. Thumbnails are not updated automatically; they will go out of date if features are added to a data source or if the symbology of a layer changes. Thumbnails are created in ArcCatalog. Vector A coordinate-based data model that represents geographic features as points, lines, or polygons. Each point feature is represented as a single coordinate pair, while line and polygon features are represented as ordered lists of vertices. Attributes are associated with each feature, as opposed to a raster data model, which associates attributes with grid cells. x,y coordinates A pair of values that represents the distance from an origin (0,0) along two axes, a horizontal axis (x) representing east-west, and a vertical axis (y) representing north-south. On a map, x,y coordinates are used to represent features at the location they are found on the earth's spherical surface. Section 1

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