Surveying GIS: Developing a new GIS, Part 4.
Once we establish our data model, what do we do with it? It’s about the data, right? So how do we work with data in our new GIS? Let’s look at how the data model works.
In this process, we first need to develop our data model. Next, we need to acquire our data. Then we need to put that data someplace where we can manage it and use it effectively. We require a container for the data in our model before it can become useful as GIS data. In this example, we will create and load a standard ESRI geodatabase (.gdb) file.
1. Identify the information products that you will create and manage with your GIS.
2. Identify the key data themes based on your information requirements.
3. Specify the scale ranges and spatial representations of each data theme at each scale.
4. Decompose each representation into one or more geographic data sets.
5. Define the tabular database structure and behavior for descriptive attributes.
6. Define the spatial behavior and integrity rules for your datasets.
7. Propose a geodatabase design.
8. Design editing workflows and map display properties.
9. Assign responsibilities for building and maintaining each data layer.
10. Build a working prototype and review and refine your design.
11. Document your geodatabase design.
In ArcCatalog, we navigate to the folder in the catalog tree where we want to locate our new geodatabase and right-click on it. We then click on “New.” In ArcGIS 9.2 and newer versions, there are two geodatabase choices: Personal or File Geodatabase. Let’s choose File Geodatabase. A new folder appears in the tree. We now name our new geodatabase. (See Figure 4.)
We will select “Feature Class (single).”3 This action brings up the “Import” dialog box. In the top box, “Import Features,” click on the file icon and navigate to the data source you wish to import. The data source can be Shape files, coverages or CAD files. In the “Output Feature Class,” give it a unique name. You can select only the portions of the data set you wish to import by using the “Expression” button, which activates the “Query Builder.” You can also add or delete fields from your “Output Feature Class” using the “+” or “X” buttons in the dialog. Click “OK” to import your new feature class. (See Figure 5.)
ArcGIS uses a standard computer SQL (Structured Query Language) for accessing and managing its databases. SQL is not used to add or delete any data in ArcGIS. But there are a variety of ways SQL Expressions are used in ArcMap and ArcCatalog to manipulate data. In ArcGIS, the dialog for creating an SQL Expression is the Query Builder.
Then in the data frame, right-click on the layer we want to query. From the menu, choose “Properties” then “Definition Query.” Then click the “Query Builder” button. (See Figure 7.)
Using GIS tools to view our data in this dynamic fashion is called geovisualization.5 This process demonstrates the power of working with geographic data in a system as opposed to viewing it on a two-dimensional analog map product.
Now that we have our GIS data all neatly organized in a container, what’s next in our plan? Our data may be ready for our users, but are our users ready for our data? That will be determined in the training plan--the next installment of this series to be explored in August.
References1. This online file can be accessed from the Help menu in ArcGIS 9.2.
2. If you need to refresh ArcCatalog basics, review the article “Data management with ArcCatalog,” POB, April 2006.
3. A feature class is 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 be stored in geodatabases, Shape files, coverages or other data formats. 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.
4. A feature data set is a collection of feature classes stored together that share the same spatial reference.
5. Geovisualization (short for geographic visualization) refers to techniques and tools designed to interactively “visualize” spatial phenomena.
To view the first three installments of this series, visit www.pobonline.com and search on “Developing a New GIS.”