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Data queries are fundamental in GIS projects, serving as essential tools for data preparation and final analysis. This guide covers various types of queries, including attribute, spatial, and raster data queries, utilizing SQL syntax for effective data selection. Learn about query expressions, Boolean logic, and combining conditions to filter data accurately. Explore methods for spatial feature selection, saving selections as new data files, and manipulating selected features within ArcMap. Gain the skills to optimize your analyses with powerful querying techniques.
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Data Queries Selecting features in ArcMap
Data queries • Important part of a GIS project • Can be a part of your data preparation or final analysis • Data Queries (selecting data based on a question or criteria) • Attribute Query • Spatial Data Query • Raster Data Query
Attribute Data Query • SQL (Structure Query Language) is used select records from an attribute table • Structure (syntax) of the query language • Select <attribute> (select field or column) • From <relationship> (defines a table) • Where <condition> ( some condition or criteria) Selectname Fromcounties Where name= Monterey • Query Expressions • Boolean expressions • Combination of field, a value, and a logical operator (=, +, - , etc..) • Boolean connectors (AND, OR, XOR, NOT) • Connects two expressions Select from the “name” field in the “counties” table, where the values=“Monterey”
Query Expressions • Boolean Expression • Combination of field, value, and an operator • Name = Monterey • Pop2000 >=400,000 • State_Name= Calfornia • Boolean connectors • Keywords that connect two expressions • State_Name = California AND Pop2000>= 400,000 • State_Name = California OR Pop2000>= 400,000
Query Expressions – Boolean Connectors - AND • State_Name = California AND Pop2000 >= 400,000 • AND - satisfy both criteria - intersection
Query Expressions – Boolean Connectors - OR • State_Name = California OR Pop2000 >= 400,000 • OR - satisfy either one or both criteria - union
Spatial Data Query 3 Ways to select features spatially • Feature selection by cursor - (select features tools) • Feature selection by graphic - (draw a graphic and use it to select features) • Feature selection by spatial relationship • Containment (fall within a feature) • Intersect (intersect a feature) • Proximity ( within a specified distance)
Working with selected features • create new selection • add to currently selected features • remove from currently selected features • select from currently selected features You can add, remove or select from currently selected features using location and attribute queries.
Isolating your selected features • Permanently save your selected features • save as new data file (shapefile or geodatabase) • Right-click on layer data Export data • Temporary save your selected features • create a temp layer in your ArcMap project as • Right-click on layer selection create layer from selected features • One extra step …. • --- to create a .lyr file • Right-click on layer Save As Layer File
Summary of selection types • Select by attribute using SQL • In ArcMap you can find this in the: • Selection menu • Attribute table • Definition query – displays data only • Located in the layer’s properties • Spatial Query: • Manually using the cursor • Select by graphics • Select by Location dialog
