Geographic Information System/Selection
General Information
[edit | edit source]The select tool can be used in a variety of ways while using GIS. The purpose of the tool is to allow someone to highlight and work with a smaller portion of the map rather than the whole thing at once. Applying a selection lets you specify the features you want to calculate statistics for, view attributes for, edit or define the set of features that make up a layer. The two most common ways are by either selection by location, or selection by attribute. Another option is to choose the "Select Features" button, where you are able to choose from a list of different options that allow you to draw your own selection. This is done by clicking the left mouse each time you want to create a new point and double clicking once the shape is of satisfaction (in the case of select by polygon being chosen).
Select By Attributes
[edit | edit source]To open the "select by attributes" dialogue box, click on "Selection" then "Select by Attributes." Once in the dialogue box, you must then choose which layer you want to preform the selection on. Next, you must choose the method in which you would like to perform the selection, for example, the first option being "Create a new selection." There are a number of different expression building tools which will then allow you to create a query expression. This is where you build an expression to choose which attributes in a certain layer you would like to select and later work with. This would be a good choice if you were working with something such as population for example.
Select by Location
[edit | edit source]This is one of the other main select tools used in GIS. The "Select by location" tool allows you to select a certain location based on where it's location compared to features in different layers of the map. For example, if you wanted to see how many homes were affected by a flood, you would be able to select all the homes that fell within the flood boundaries. Once again, to reach the tool, you start by clicking "Select" then "Select by location." Once the dialogue box is open, the first step is to choose the type of selection that you would like to make. Next, choose the target layer(s) that you would like to use for the selection. There is then a long list of different spatial relationship rules that you have to choose from. Choose the one which best fits what you are searching for. After this, you must specify the source layer which will be used to create the selection.
Using the Selected Features
[edit | edit source]By clicking "Selection" on the main menu, there are a number of different options available to you which allow you to interact with the selection that you have made. Some of these options include zooming to the selected features, clearing the selected features, and calculating statistics for the field values of whatever has been selected. One is also able to export the selection as a data set. To do this, choose data, export data, and then in the drop-down menu choose to export only the selected features. If you have certain features selected on you map, they will also be selected in any tables or graphs that you open with that data present. One other very useful tool in the selection menu is the ability to create a layer from your selected features. This can be done by right-clicking on the original layer that the selection is from, going to the selection menu, and choosing "Create Layer From Selected Features."