Editing data in ArcMap

Aside from the ability to view and analyze geographic data, many GIS applications also contain tools that enable data editing. ArcMap contains powerful tools that facilitate editing either graphically on the map, or through tabular or computational editing.

For editing to take place, an editing session needs to be started. By default, editing is turned off when something is being viewed through ArcMap to protect against accidental changes to the data. However, when updates or revisions need to be made, an editing session can be started by turning on the Editor Toolbar, then clicking on Editor > Start Editing. This enables changes to be made to data.

Once edits are made, you will need to click on Stop Editing, which will give you the option to save or discard the changes.

How to make edits will depend on what data needs to be changed. On the Editor Toolbar, there is a list of possible tasks to choose from, as well as a target layer to which the changes will be applied. There is also a Sketch Tool, along with a number of other tools for producing various geometries. The Attributes and Sketch Properties allow viewing of data in tabular form.

For example, if an existing polygon needed to be divided into two sections, the correct task, target, and feature need to be specified, and a dividing line needs to be drawn. To do so, under Task, select Modify Tasks > Cut Polygon Features. Choose the correct target layer, then make sure the Edit Tool is selected, then click on the polygon that needs to be split. Now, click on the Sketch button , and click a location to start drawing the dividing boundary. To add additional points, click elsewhere on the map. To finish drawing, double-click on the final point. If the line drawn produces a valid polygon cut, the new section will flash and become a new feature.

Tip: A useful feature of Editor Mode is the Snapping feature. Snapping can be activated to cause the cursor to automatically land ("snap") on a nearby point or line when it is within a few pixels. This is helpful when the sketch that you are trying to draw must correspond to certain edges or vertices. To activate Snapping, click on Editor > Snapping..., which opens a panel. At the top, you can select which items to snap to in various layers, and at the bottom, you can specify other snapping options. The Edit Sketch refers to the new sketches that you make while in the current editing mode.