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.