Unit 6 – Lesson 3: Queries Civil 3D 2010 Student Workbook ▪ 1 Queries Overview The basis of a GIS (Geographic Information System) is geospatial feature data that is linked to a database. Records in the database are linked to a feature such as a point, line, polygon, or raster cell. For example, a parcels database can have attribute data that lists the owner, the address, and the value of the property. Either the geospatial features or the database can be queried to find a subset of particular interest. In some cases, you may want to bring in all the data in a certain geographic area by drawing a rectangle or a circle on the base map. This is a type of location-based query. In other cases, you may want to find a specific subset of a data layer, such as all parcels with value greater than a certain amount. These are called property-based queries. The following illustration shows an empty grid on the left, a location-based query in the center, and a property-based query on the right. Lesson 3 AutoCAD Civil 3D 2010 Education Curriculum Student Workbook Unit 6: Geospatial DataUnit 6 – Lesson 3: Queries Civil 3D 2010 Student Workbook ▪ 2 Objectives After completing this lesson, you will be able to: - Discuss the different types of queries. - Perform spatial queries from feature sources. - Perform data queries from feature sources. - Combine queries. Exercises The following exercises are provided in a step-by-step format in this lesson: 1. Perform a Spatial Query 2. Perform a Data Query 3. Perform a Compound Query About Queries A query is a method to find specific data based on criteria. In GIS, you can query the geospatial property, or location, of a feature, or you can query the linked database of the data layer to find the data that fits the criteria. Queries are organized in a specific fashion using an underlying language called SQL (Structured Query Language). Criteria detail specific conditions about the desired subset; for example, an attribute must be greater than a value, or the features must lie within a specified rectangle. Examples of criteria for a location-based query are “find the points inside of this polygon,” or “find the parcels that are within 250 feet of the centerline of this road.” An example of a criterion for an attribute- or property-based query is “find the parcels that have a value greater than $250,000.” Either type of query results in a selected subset of the data layer. The following illustration displays the result of a query.Unit 6 – Lesson 3: Queries Civil 3D 2010 Student Workbook ▪ 3 Queries can also be put together into a compound query. The compound query can use binary operators such as AND and OR to logically sequence the compound query. If two conditions are linked with AND, then both conditions must be true for the feature to be placed in the subset. If two conditions are linked with OR, then if either condition is true, the feature is placed in the subset. The Create Query dialog box contains many options for building simple or compound queries. About Filters A filter uses a query to restrict the viewable data. A spatial filter can be used when importing data from another file format. You can specify (or limit) the area into which incoming objects are imported. A filter can also be applied based on the value of an attribute. For example, the data layer of all counties in the U.S. could be filtered for the counties in the Commonwealth of Virginia. Filters are useful because geospatial data layers can often cover larger areas, or they may contain more data than necessary for a project. It is common to require only a subset or section of the data available. Using a filter can help you improve performance when working with large sets of feature data. A spatial filter can be used to display only records that are linked to features selected in the drawing. When a spatial filter is applied, the Data View displays only those records that are linked to selected objects in the drawing, as shown in the following illustration.Unit 6 – Lesson 3: Queries Civil 3D 2010 Student Workbook ▪ 4 Key Terms Query A query is a method to find specific data based on criteria. In GIS, you can query the geospatial property, or location, of a feature, or you can query the linked database of the data layer to find the data that fits the criteria. SQL Structured Query Language Location-Based Query A query based on the spatial attribute of a layer. Property-Based Query A query based on values of a property (attribute) in a layer’s database. Filter A filter uses a query to restrict the viewable data. Compound query A compound query links two or more query criteria using binary operators such as AND and OR to logically sequence the criteria.Unit 6 – Lesson 3: Queries Civil 3D 2010 Student Workbook ▪ 5 Exercise 1: Perform a Spatial Query In this exercise, you perform a spatial query to display the data required for the project. At the end of this exercise, the drawing displays as shown. For this exercise, open …\I_Query-EX1.dwg (M_Query-EX1.dwg). 1. From the status bar, change your workspace to Tool-based Geospatial. 2. On the View tab of the ribbon, Palettes panel, click Map Task Pane. The Task Pane window displays. 3. On the Home tab of the ribbon, Data panel, click Connect. The Data Connect Window displays. 4. In the Data Connections by Provider window, click Add Raster Image or Surface Connection. You now navigate to the location of the Raster Data. There are two buttons shown under the Source file or folder. If you are connecting to a single image, use the File button. For multiple files, use the Folder button. 5. For Connection Name, enter Project Aerials. 6. Click the Folder button. 7. Navigate to the Raster Data folder. Click OK. 8. Click Connect. The connection to the Raster Data folder is added. In the Add to Map section of the Data Connect box, the images in the folder are listed. 9. Right-click any image. Click Select All.Unit 6 – Lesson 3: Queries Civil 3D 2010 Student Workbook ▪ 6 10. Click Add to Map. The raster image data is displayed and listed in the Task Pane. 11. In the Data Connections by Provider, click Add SHP Connection. 12. For the
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