Final GPS Exam Study Guide

Identify the 3 segments of GPS

• Control – ‘brain’ of the system
• Controller monitors system and sends adjustments if necessary.
• The DoD operates this segment from Falcon Air Force Base in Colorado Springs, Co.
• Also, 4 monitoring and upload stations throughout the world.

• Space
• NAVigation Satellite Timing And Ranging
• Fully operational system consists of at least 24 satellites
• Constantly being ‘commissioned’ and ‘decommissioned’
• 20,200km above earth, one revolution every 12 hours

• User
• GPS receivers on the ground
• Civilian users outnumber military. Many applications.
• Emergency Services, Public Safety, Recreation, Asset Management, Routing, Agriculture, Vehicle Tracking

List the acceptable number of satellites (SV's - space vehicles) for an accurate 3D position.

• GPS position is calculated by Trilateration, measuring of the distance from at least three satellites to establish a position on earth.
• Four for an accurate 3D postion.
  
• Trigonometry requires three perfect measurement to define a point in three-dimensional space. However, the accuracy of a measurement based on three satellites may be diminished due to the non-synchronization of clocks in the GPS satellites and receivers.

List and explain sources of error in the GPS system

• Selective Availability – turned of in May of 2000
• Obstructions – buildings, vegetation
• Multipath – GPS signals reflecting off objects
• Atmospheric delay
• Worse during the heat of the day
• Worse when satellites low on the horizon
• GPS works in all weather conditions

Explain why satellites are provide a good system for locating positions on the earth

• Accurate position can be determined without having a direct line of sight between the known and unknown location.
• Only need a clear view of the sky
• Can determine accurate position almost anywhere at anytime on the earth.

Define trilateration

• GPS position is calculated by Trilateration, measuring of the distance from at least three satellites to establish a position on earth.
• Four for an accurate 3D postion.
  
• Trigonometry requires three perfect measurement to define a point in three-dimensional space. However, the accuracy of a measurement based on three satellites may be diminished due to the non-synchronization of clocks in the GPS satellites and receivers.

Discuss how the distance from the satellite to the GPS receiver is determined.

• Two factors involved in measuring the distance from a satellite.
• The speed of the radio signal (the speed of light = 300,000 km/sec)
• The time it takes the signal to reach the earth
• Each GPS satellite transmits data that indicates its location and the current time.
• All GPS satellites synchronize operations so that these repeating signals are transmitted at the same instant.
• The distance to the GPS satellites can be determined by estimating the amount of time it takes for their signals to reach the receiver.

Describe the almanac and what it is used for

• Set of parameters used to calculate the general location of each satellite.
• The almanac specifies where each GPS satellite will be at any given moment in the near future.
• Almanacs are used for planning the best time to collect GPS data and for quick acquisition of satellite positions by the receiver.

Define ephemeris information and what it is used for

• The orbits of all GPS satellites are measured constantly by the DoD.
• They determine satellite ranging and calculate the exact location of each satellite.
• The adjusted measurements are transmitted from the DoD to the satellites
• These minor corrections are then transmitted by the satellites as ephemeris information.
• The ephemeris information is a data file that contains orbit information for one particular satellite.
• Information used by the GPS receivers along with their internal almanac to establish precisely the position of a satellite.

Define autonomous GPS

• GPS without some form of data processing to insure accuracy (not corrected in the field). It is accurate to +/- 10 M.

Describe differential GPS (SBAS, WAAS, Post-processing)

• The precise measurement of the relative positions of two receivers tracking the same GPS signals.
• One receiver places at a ‘base’ station over a know coordinate
• Other receivers (rovers) use the corrected GPS information to eliminate error in their measurements
• The ‘base’ station receives the same GPS signals as the roving receiver but instead of working like a normal GPS receiver it attacks the equations backwards.
• Instead of using timing signals to calculate its position, it uses its known position to calculate timing.
• It figures out what the travel time of the GPS signals should be, and compares it with what they actually are. The difference is an "error correction" factor.
• The base receiver then transmits this error information to the roving receiver so it can use it to correct its measurements.
• Wide Area Augmentation System
• FAA’s strategic objective of a seamless satellite navigation system for civil aviation.
• WAAS is based on a network of approximately 25 ground reference stations that covers a very large service area.
• Signals from GPS satellites are received by wide area ground reference stations (WRSs).
• Each of these precisely surveyed reference stations receive GPS signals and determine if any errors exist.

Define GPX

• GPX, or GPS eXchange Format is an XML schema designed for transferring GPS data between software applications. It can be used to describe waypoints, tracks, and routes. The format is open and can be used without the need to pay licence fees.

What is a waypoint?

• Waypoints are sets of coordinates that identify a point in physical space. For the purposes of terrestrial navigation, these coordinates usually include longitude and latitude, and sometimes altitude (particularly for air navigation). Waypoints have only become widespread for navigational use by the layman since the development of advanced navigational systems, such as the Global Positioning System (GPS) and certain other types of radio navigation. Waypoints located on the surface of the Earth are usually defined in two dimensions (e.g., longitude and latitude); those used in the Earth's atmosphere or in outer space are defined in at least three dimensions (four if time is one of the coordinates, as it might be for some waypoints outside the Earth).

Describe the critical software settings in Trimble TerraSync

• PDOP = Position Dillution of Precision = 6 or higher (Measure of the geometry of the satellites in the sky)
• Elevation Mask = 15 degrees or more (Satellites must be 15 degrees or more above the horizon or they are not used)
• SNR = Signal to Noise Ration = Less than 39 (measure of the strength of the signal)

What is an .ssf file?

• The native format for data files stored on Trimble GPS units. It stores attribute information beyond what a recreational GPS could store.

Describe what Trimble Pathfinder Office is used for.

• Pathfinder Office is used to construct data dictionaries as well as to post-process data collected on Trimble units in the field. Pathfinder Office also aids in transferring files to and from the Trimble unit.

Describe several differences in a professional grade GPS like the Trimble GeoXT and a recreation grade GPS like the Garmin

• Professional grade GPS devices allow the user to filter for accuracy.
• Professional grade GPS devices allow data to be post processed.
• Professional grade GPS devices have a higher accuracy rate.
• Professional grade GPS devices allow for attributes to be stored during feature collection.
• Professional grade GPS devices allow for data to be collected through the use of offsets.
• Professional grade GPS devices allow for data to be collected through a greater variety of means.
• Professional grade GPS devices can be loaded with different operating environments to meet the needs of the user.

Exam 2 Study Guide

1. Define an attribute domain.
   
• In a geodatabase, a mechanism for enforcing data integrity. Attribute domains define what values are allowed in a field in a feature class or nonspatial attribute table. If the features or nonspatial objects have been grouped into subtypes, different attribute domains can be assigned to each of the subtypes.
  
  
• What are the 2 types?
• Coded-value and range
  
  
• How are range domains validated?
• Range domains are validated in an editing session through the Editor toolbar.
  
  
• What are split and merge policies?
• Split and merge policies define how the values of a field will react once a feature is split or merged (i.e. are the values added, is the highest selected, does the field defer back to the default value). Split policies include default value, duplicate, and geometry ratio. Merge policies include default value, sum value, and weighted average.
• 
  
  
2. Define a subtype.
• What data type must the field be to apply a subtype to it?
• In geodatabases, a subset of features in a feature class or objects in a table that share the same attributes. For example, the streets in a streets feature class could be categorized into three subtypes: local streets, collector streets, and arterial streets. Creating subtypes can be more efficient than creating many feature classes or tables in a geodatabase. For example, a geodatabase with a dozen feature classes that have subtypes will perform better than a geodatabase with a hundred feature classes. Subtypes also make editing data faster and more accurate because default attribute values and domains can be set up. For example, a local street subtype could be created and defined so that whenever this type of street is added to the feature class, its speed limit attribute is automatically set to 35 miles per hour.
  
  
• Objects in an object class and feature in a feature class may be further subdivided into subtypes.
  
  A subtype is a special attribute that lets you assign distinct simple behavior for different classifications of your objects or features. All subtypes of a class share the same set of attributes.
  
  The motivation for defining subtypes of an object class is to introduce a lightweight subdivision of an object class that adds these capabilities:
• You can name subtypes to describe each member of a classification of your objects.
• You can define distinct attribute domains for each field in a subtype.
• You can define distinct default values for each field in a subtype.
• You can prescribe the types of relationships that are possible between the objects in a subtype and objects in another subtype in the same or different object class.
• If you write some software code, you can also add custom rules for subtypes of object and feature classes.

An object class does not have to contain subtypes. If none are defined, you can still set attribute domains, default values, and rules - but on the object or feature class as a whole instead of a subtype.

• Subtypes are only permitted on Long Integer fields
  
  
• Why do we create subtypes?
• What are the advantages?
• Subtypes increase data integrity and can speed data entry.
  
• p. 88 in the text
1. Describe the spatial adjustment process in ArcMap for transforming data from one coordinate system (or non-real world coordinates) to another coordinate system.
• Georeferencing is used for CAD files and for images. When these are in non-real world they must have real world coordinates to display correctly. A world file is created with the same name as the image or CAD. When these are displayed in ArcMap, the world file is used to provide the coordinates. Georeferencing builds the world file.
  Spatial adjustment is a tool used in an editing session for vector feature classes to actually update the data with coordinates. These are three processes that can be used - transformation, rubbersheeting and edgematching. In class we used transformation. This used control points - coordinates that had been collected with a GPS unit. Because this is done in an edit session one can use tools such as snapping to improve the process.
  
  
2. Describe how CAD data is represented in ArcMap. Also see: Contents of CAD drawing.
   
• Define CAD feature datasets
• CAD feature datasets are an ArcGIS feature data object representation of a CAD drawing. They contain a collection of CAD feature classes that allow you to interact with CAD data in ArcGIS similar to how you would with geodatabases and shapefiles. This includes performing operations such as attribute query, symbol modifications, and conversion. However, CAD feature datasets are read-only, so their feature geometry and attributes cannot be edited.
  
  
• Define CAD feature classes
• CAD feature classes are homogeneous collections of CAD features of the same geometry type that possess a common set of attributes. Typical feature classes are geographical representations of features as points, lines, polygons, and multipatches; they can also be map text (annotation). All CAD feature class types will always exist in a CAD feature dataset, even if a feature class does not contain any features. You cannot add CAD feature classes to a CAD feature dataset.
  
  
• Define CAD drawing datasets
• CAD drawing datasets are a unique representation of a CAD drawing. They contain all the contents of the CAD drawing. This means that all geometries are organized into a single layer. This design allows you to work with a CAD drawing file as one entry in the catalog or map, similar to how you work with a drawing file in a CAD program.
  
  CAD drawing datasets reside within a CAD feature dataset and are denoted by a white compass icon. They are rendered using the original colors of the CAD entities. They have limited functionality when you compare them to CAD feature classes. You can turn drawing layers on and off, perform coordinate transformations, and modify the display effects (brightness, contrast, and transparency). However, you cannot change their symbols, perform spatial or attribute queries, or use them as a snapping layer.
  
  
• Understand the differences - which do we use to import to a GIS data format? Which one can we change the symbology of?
  
  
3. Describe what makes features smart. (chapter 5 in the text)
   
   
4. How do we progressively add intelligence to features in the Geodatabase?
   
   
5. What is the importance of the Spatial Reference in ArcGIS? XY domain in the Geodatabase? How is this different than with a Shapefile?
• XY DOMAIN - In Geodatabases, you have to specify the an XY domain for your feature classes. The XY Domain is the 'bounding coordinates' that your features can fall within. If you try to put a point, line, or polygon on the map that is outside these bounding coordinates, it will not let you add the geometry. You can not alter the XY domain after you create it so you must plan for as big as your data may grow geographically.
  
  Shapefiles do not require specifying an XY domain. You can create a shapefile and add a point in Asheville and one in Paris and one in India. The shapefile does not have a bounding box of coordinates the data must fall into. You can put points literally anywhere in the world.
  
  The underlying reason the geodatabase using the XY Domain, and we did not discuss this, has to do with how it stores data and allows the geodatabase to store more precise data because of the XY domain.
  
  
6. What do you know about Raster Catalog's
• A collection of raster datasets defined in a table of any format, in which the records define the individual raster datasets that are included in the catalog. Raster catalogs can be used to display adjacent or overlapping raster datasets without having to mosaic them together into one large file. In ArcView 3.x, raster catalogs were called image catalogs.
  
  Raster catalogs can be constructed from varying imagery types and resolutions. The imagery is referenced rather than mosaicked.
  

Digitizing

At the moment, work on the database is revolving primarily around digitizing the roads and sidewalks on campus. We declared domains and subtypes for the sidewalks in order to get practice with streamlining data creation.

Update on the Campus Geodatabase

Here's the latest update on the campus geodatabase.
We have been converting our CAD data into polyline data within our geodatabase and then converting the associated buildings into polygons. As there is a significant difference between our CAD data and the orthophotos, a lot of data will need to be digitized manually.

Geodatabase Structure

I just wanted to throw up a quick post as to capture the evolution of our class geodatabase. We began initial work on 2-October and the graphic below captures the organization thus far. At this point we are building our geodatabase without a predefined structure, and I will be doing my best to capture the relationships and dependencies that we find to be necessary as we move along in the process.

Study Guide - Notes Prior to Exam

Pages to study 14,15,18, 26, 29, 38, 47, 58, 185

Attributes - Pieces of information that describe features on a map.
Attributes include descriptive strings, coded values, discrete numeric values, real numeric values, and object identifiers.

Database schema - The structure or design of the database including relationships, organization, and compositional data.
ArcCatalog is a database schema editor.

Data Model - Abstraction or representation of the real world.
Data models are important as they determine database design.

Domain - per ESRI dictionary - The range of valid values for a particular metadata element.
This is typically in the form of a dropdown list in a geodatabase.

Feature Dataset - Multiple feature classes that participate in some sort of topological relationship.

Geodatabase - Object-relational geographic data. Provides a centralized location for storing all GIS data.

GIS Golden Rule - For every one feature of a map there is one record in the attribute table. Multi-part features do exist and are an exception to this.

Map surrounds - External features in the map layout view (legends, north arrow, scale bar, etc.).

Objects - Features (i.e. trees). Object-based data models attempt to factor in their real-world behavior. Their behavior is dependent on other objects.

Object Based Data Model - Data model including all real-world relationships.

Picture Rasters Data - A photograph used in the construction of maps (i.e. real estate advertisements).

Spectral Rasters - Usually refer to aerial orthophotography.

Subtypes - per ESRI dictionary - In geodatabases, a subset of features in a feature class or objects in a table that share the same attributes. For example, the streets in a streets feature class could be categorized into three subtypes: local streets, collector streets, and arterial streets. Creating subtypes can be more efficient than creating many feature classes or tables in a geodatabase. For example, a geodatabase with a dozen feature classes that have subtypes will perform better than a geodatabase with a hundred feature classes. Subtypes also make editing data faster and more accurate because default attribute values and domains can be set up. For example, a local street subtype could be created and defined so that whenever this type of street is added to the feature class, its speed limit attribute is automatically set to 35 miles per hour.
Subtypes are used to enhance performance

Thematic Rasters - Look at a specific phenomenon of an area (Landsat, slope).

TINs - Triangular Irregular Networks.
Display surfaces vector-based information. Creates triangles from coordinates position changes between points. TINs are a more efficient way of displaying surface information.

Topology - Spatial relationships between features
Having topology built into geodatabases speeds up spatial queries.

CGIA - Center for Geographic Information and Analysis

GSDI - Global Spatial Dataset Infrastructure

FCDC - Federal Geographic Data Committee

NCGICC - North Carolina Geographic Information Coordinating Committee
Responsible for setting standards in North Carolina.

OGC - Open Geospatial Consortium
Group working toward standardization of GIS models.

UML - Unified Modeling Language

Ways that data can be accessed in ArcGIS.
* Data access objects
* Non-topological features
* Through relational database system (i.e. Access)

Geodatabase design can be divided into 2 categories:
Logical - Our perception of geodatabase layouts. This is an interative process that all stakeholders need to be involved with design.
Physical - Actual database as realized in implementation.

Data models are moving toward increased interoperability. There is an innate problem with data portability due to the complex relationships and functionality built into data models.

Do not use spaces in file or directory names (this will eliminate a large number of errors). All data should ideally be managed within ArcCatalog in order to ensure that all data components are moved in unison. Standardized directory structures are important when dealing with larger volumes of data. File management should be a component of project design from the beginning.

We convey information through discrete objects or as raster data. Surfaces can be modeled with rasters or with TINs (triangular irregular networks).

There are a number of ways to visualize data by differentiating between attributes. Numeric data can be visualized using a number of classification schemes.

Maps exhibit spatial relationships.
* Connectivity
* Containment
* Adjacency

Layers are referenced in the map document they are not an integral component of the documents.

CAD data was the first generation data model.

Coverages are georelational data models. Multiple feature classes can be contained within a coverage, but they must be spatially related. Coverages store topology in tables. Topology was big advantage of the coverage data model. Coverages were a dominant force in GIS for 20 years. Coverages kept track of shared geometry as opposed to the coincident geometry found in geodatabases and shapefiles. Coverages cannot contain "donut" shapes or overlapping shapefiles. In coverages the "info" folder contains attributes for all features. You must use ArcCatalog to move coverages.

Shapefiles are not topological. Shapefiles must contain *.shp, *.dbf, and *.shx files. The *.shp contains the actual shape geometry, the *.dbf file is a table with all of the shape's attribute information, and the *.shx file links both of these files together. *.prj files contain the shapes relevant projection and coordinate system information. Shapefiles store single feature types that are thematic in nature. Some topological type information can be simulated through ArcGIS as the software is able to determine spatial relationships between shapefiles (this allows for queries concerning multiple shapefiles to be run). Shapefiles have limited abilities to enforce data integrity (no domains). Shapefiles do not automatically recalculate length and area.

File geodatabases are recommended over personal geodatabases. They are not stored in a conventional relational database system (Access). Personal geodatabases are limited to 2GB in size. Personal and Workgroup Scalable Geodatabases are limited to 4GB in size. File geodatabases are limited to 1TB per table (this can be expanded to 256TB). Scalabe geodatabases are capable of versioning, simultaneous editing, historical archiving, as well as check-in/check-out editing scenarios.

Building a Geodatabase Screen Shot

Here is a screen shot from the Building a Geodatabase exercise. This screen shot show the annotation that was added to the map as part of the exercise.

Editing a Geodatabase Screen Shots

Here are a couple of screen shots from the Editing a Geodatabase exercise. The exercise involved editing networks in a geodatabase as well as working with domains and subtypes from the ArcMap interface. The first screen shot depicts some of the topological edits that were made to existing parcel dimensions.

As can be seen in the second screen shot "dimensioning" was also used.

Class 4 Notes Continued

1. Define the geodatabase.
The geodatabase (or geographic database) is similar to the ESRI coverage data model as a container in which to store data. They are three types of geodatabases used in ESRI products that can be selected for a varying data requirements. ArcGIS sotware is based around the concept of a geodatabease. The geodatabase is a more powerful data model than other alternatives offered by ESRI and allows users to form complex relationships between data as well as providing tools to streamline data entry and query construction.

2. List the elements of the geodatabase.
Some of the elements of the geodatabase include (as per the ESRI documentation)

• Annotation - A specialized feature class that stores text or graphics that provide information about features or general areas of a map. An annotation feature class may be linked to another feature class so that edits to the features are reflected in the corresponding annotation (i.e., feature-linked annotation).
• Cadastral Fabric - A cadastral fabric is a seamless parcel boundary network, which is created and maintained using data from survey records.
• Dimension - A special type of geodatabase annotation that shows specific lengths or distances on a map. A dimension feature may indicate the length of a side of a building or land parcel, or it may indicate the distance between two features such as a fire hydrant and the corner of a building.
• Feature Class - A collection of geographic features with the same geometry type (i.e., point, line, or polygon), the same attributes, and the same spatial reference. They allow homogeneous features to be grouped into a single unit for data storage purposes; for example, a feature class of city streets.
• Feature Dataset - A collection of feature classes stored together that share the same spatial reference. Feature classes in a feature dataset share a coordinate system, and their features fall within a common geographic area. Feature datasets are used to help model spatial relationships between feature classes.
• Geometric Network - Edge and junction features that represent a directed-flow system network, such as a utility or hydrologic system, in which the connectivity of features is based on their geometric coincidence.
• Network Dataset - A collection of topologically connected network elements (e.g., edges, junctions, and turns) that are derived from network sources, typically used to represent an undirected-flow system network such as a road or subway system.
• Raster Catalog- A collection of raster datasets defined in a table of any format, in which the records define the individual raster datasets that are included in the catalog. Raster catalogs can be used to display adjacent or overlapping raster datasets without having to mosaic them together in one large file.
• Raster Dataset - Any valid raster format organized into one or more bands. Each band consists of an array of pixels (cells), and each pixel has a value (e.g., a Landsat satellite image).
• Relationship Class - A class similar to relationships that exist within an RDBMS. Relationship classes manage the associations between objects in one class (e.g., table or feature class) and objects in another. Objects at either end of the relationship can be features with geometry or records in a table.
• Schematic Dataset - A dataset used for graphically representing network connectivity and sets of relationships.
• Survey Dataset - An integrated collection of specialized survey feature classes and associated survey measurements.
• Table - A set of data elements arranged in rows and columns. Each row represents a single record. Each column represents a field of the record. Tables typically store stand-alone attribute information or information associated with a spatial location such as addresses.
• Terrain - A triangulated irregular network (TIN)-based dataset that uses feature classes as data sources to model multiple resolution surfaces using z-values.
• Toolbox - A collection of dataflow and workflow processes for performing data management, analysis, and modeling.
• Topology - The arrangement that constrains how point, line, and polygon features share geometry within a geodatabase. For example, street centerlines and census blocks share geometry, and adjacent soil polygons share geometry. Topology defines and enforces data integrity rules, topological relationship queries and navigation, and sophisticated editing tools. It also allows feature construction from unstructured geometry.

3. Describe how the geodatabase is different that other spatial data formats in it's handling of 'real-world' behaviors.
The geodatabase implements several data integrity validation tools that allows the users to enforce 'real-world' behavior patterns through pre-defined 'templates'. Unlike ESRI's other available data formats 'real-world' behavior is enforced by limiting the range of potential user inputs through subtypes, domains, and default values to feature classes.

4. Describe the types of geodatabases available at 9.2.
ArcDesktop 9.2 uses three types of geodatabases, the personal, the file, and the ArcSDE geodatabase. The personal geodatabase is based on the MS Access relational database model and is limited to 2 GB of data. It is not very robust and is limited in its multiuser editing capabilities. The file geodatabase is based on a SQL relational database model and can handle up to 1 TB of data. It requires no additional software other than the ArcDesktop program. In this type of geodatabase each data set is stored in a separate file as opposed to the personal geodatabase which stores all datasets in a single *.mdb file. The file geodatabase is the recommended native format for ArcGIS. The ArcSDE geodatabase requires an additional relational geodatabase software package such as Oracle and SQL server. It is employed for enterprise solutions and its upper limits are dependent on the software package upon which it is based.

Class 3 Notes

First off, I stumbled across a fun use for Google Earth. Check out PlaceSpotting.com. It provides a riddle and you have to try to find the location of the place featured in the riddle with Google Earth. Okay so it might only be fun if your a Google Earth nerd.

Study Questions:
1. Why might you use 'connect to folder'?
Connecting to a folder keeps you from having to repeatedly having to locate a data folder that is nested in a series of subfolders. It's more or less a time-saver and insures that you save your data to the same spot consistently.

2. What is an alias and why would you use one?
An alias is a name for a field, table, file, or dataset that is more user friendly. It is not the name that the software references in relationships or scripting, but is the name that users of the information will encounter under normal use. An alias avoids database naming conventions for fields, tables, files, or datasets and can be more descriptive and easy to interpret than the actual name associated with the information.

3. Does ArcMap or ArcCatalog use aliases?
ArcMap takes advantage of aliases as the end-user of a dataset will typically uses ArcMap or and ArcIMS type application to view the data (in the case of an end-user such as a city planner or sewage maintenance technician).

4. What is a domain?
Domains, or an attribute domain in the case of a geodatabase, is used to define the permissible values in a field contained within a feature class or nonspatial attribute table. If subtypes are used to group the features or nonspatial objects than separate attribute domains can be used with each one of the subtypes.

5. What is a subtype?
A subset of features contained within a feature class or objects in a table that share the same attributes is referred to as a subtype. Using subtypes can streamline data creation and can prevent the need for excessive feature classes or tables within a geodatabase. Hydrology information could be stored taking advantage of subtypes to differentiate between stream orders. Subtypes also improve accuracy because because default attribute values can be established and domains can be set up.

Article on Google's Geospatial Data

I found this article that explains how Google indexes their geographic information in Google Maps and in Google Earth. Although it is not what comes to mind when you think of GIS, it is a pretty interesting look into what is perhaps one of the largest and popular "geodatabases".

Presentations so far...

Answers to review questions unveiled

1. List 4 disadvantages of the CAD data format
CAD is designed for graphic data only, although non-CAD data can be imported via OLE into finalized drawings. GIS data can be graphic, graphics associated with data, or simply data in the form of a table.

CAD data implies no topographic relationships among data. Additionally CAD does not have a database of feature attributes associated with its geographic points (i.e. average slope of a parcel, elevation of a specific point, etc.).

Using the annontation ability of software such as that produced by AutoDesk to display attribute information creates maps that are crowded and difficult to use.

Because attribute data is not embedded with geographic data via a database, it is difficult to query a CAD drawing when attempting to perform an analysis.

2. What is a geo-relational data model?
A geo-relational data model is a model that allows spatial data to be combined with attribute data. Topological data that exists between vector features can be stored within a geo-relational data model.

3. What are 3 disadvantages to the ArcInfo Coverage?
Within an ArcInfo coverage features are generic lines, polygons, and points. A road and a powerline would appear the same and exhibit the same behavior.

Topological integrity is strictly enforced. A line cannot go through a polygon without splitting the polygon into two seperate polygons. If the edges of a feature are edited within a coverage then the topology must be reconstructed. See more about topology and coverages in the "GIS Topology" whitepaper.

Coverages create large datasets that sometimes need to be broken into smaller grids. This can make data management cumbersome and cause confusion during analysis.

4. Describe the shapefile
A shapfile stores geometry and attribute information on a single feature class. Shapefiles can overlap or be non-contiguous (a line that starts and stops again throughout a map document). The shapefile stores all of the attribute information in a dBase or *.dbf file. Shapefiles do not maintain information about topology. They differ from coverages largely because they are a single feature class (either a line, point, or polygon).

5. How many files must be present for a shapefile to be considered whole?
A Shapefile that is technically "whole" consist of three files *.shp (the shape geometery), *.shx (the index of the shape's geometery), and the *.dbf (the database file that stores attribute information associated with the shape). If these three files are intact than the shapefile is capable of being used within ArcMap. There are also additional optional features such as the *.sbn and *.sbx files that store the spatial index of the features (and similar *.fbn and *.fbx that store the same information in a read only format). The *.ain and *.aih sotre the attribute index of the active fields in a table or a theme's attribute table. The *.prj store projection or coordinate system information associated with the shape file. Metadata (which details information on who is responsible for creation of the data and other important information such as spatial attributes) is store in a *.shp.xml file. The attribute index for a a *.dbf file is stored in the form of an *.atx file.

6. What are 3 disadvantages to the shapefile?
Shapefiles do not store topology data (topology referring to special data integrity rules and the ability to support topological relationship queries and navagation). The lack of topology data results in a limited ability to enforce data integrity.

When utilizing shapfiles relationships can be defined and created within ArcMap, but they are stored within Map Documents (*.mxd) and not within the features.

Shapefiles are somewhat generic and do not have model specific behaviors (again due to a lack of topology data).

7. Describe the geodatabase in 1 sentence.
A geodatabase utlizes the Relational Database Management System (RDMS) as a container for geographic features and attributes (in addition to the relationships that exist among them).

8. List the geodatabase types.
In current versions of ArcGIS there are three types of geodatabases.

• The personal geodatabase (which is based on a Microsoft Access architecture).
• The file geodatabase.
• The scalage geodatabase (most often referred to as the ArcSDE database). The scalable database is available at three levels (personal, workgroup, and enterprise).

Datasets created within geodatabases can be transferred between the different types of geodatabase using tools available within ArcGIS desktop. See the whitepaper for more information.

9. What type of information is modeled well using raster data?
Information that is continuous (experiences gradual change over a geographic area) such as elevation, temperature, citizen income, etc is modeled using raster data. Raster data more efficiently models this change and can depict transitions through subtle shifts in color.

10. What type of information is modeled well using vector data?
Information that is discrete (exists within defined boundaries and typically depicts a geographic feature or location rather than data overlain on a geographic feature) such as telephone poles, power lines, rivers, manholes, etc is modeled using vector data. It is important to note that vector data can be resized for display at varying scales, where raster data has a definition attached to a specific scale and is distorted if the scale is reduced (the map is enlarged).

From the first day:
1. What is a blog?
A blog or a weblog is a webpage format for content that is intended to be updated on a frequent basis. The blog itself provides an easy to use format that requires only the new information be inputted into the existing format and is appended to a previously existing page. Blogs are popular for news and current events/trends type pages.

2. What is total percentage of the final grade tests are worth?
Test are worth 60% of the total final grade.