Below are some of the most common terms you will encounter when editing in ArcMap.
Editing occurs in an edit session. During an edit session, you can create or modify vector features or tabular attribute information. When you want to edit, you need to start an edit session, which you end when you're done. Editing applies to a single workspace in a single ArcMap data frame, where a workspace is a geodatabase or a folder of shapefiles. If you have more than one data frame in your map, you can only edit the layers in one data frame—even if all data is in the same workspace. Although you can edit data in different coordinate systems, it is generally best if all the data you plan to edit together has the same coordinate system as the data frame.
There are two ways to start an edit session: by clicking the Editor menu on the Editor toolbar or by right-clicking a layer in the table of contents. If you use the Editor menu to start editing on a data frame that contains data from multiple workspaces, you are prompted to choose the workspace to edit. If you right-click a layer in the table of contents, you automatically start an edit session on the entire workspace containing that layer.
Creating features is accomplished through the use of feature templates. Feature templates define all the information required to create a feature: the layer where a feature will be stored, the attributes a feature is created with, and the default tool used to create that feature. Templates also have a name, description, and tags that can help you find and organize them. If templates are not present when you start editing, they are automatically created for each layer in the current editing workspace. Templates are saved in the map document (.mxd) and the layer file (.lyr).
The terms "feature template" and "template" are used interchangeably in the Editing help.
The top panel of the Create Features window shows the templates in the map, while the bottom panel of the window lists the tools available to create features of that type. The availability of the feature creation tools, or construction tools, depends on the type of template you have selected at the top of the window. For example, when a line template is active, you can see a set of tools for creating line features. If you choose an annotation template instead, the available tools change to those that can be used to create annotation.
By default, the Line and Polygon tools create straight segments between the vertices you click. These tools have additional ways to define a feature's shape, such as creating curved lines or tracing existing features. These are construction methods, which are located on the Editor toolbar. To create a curved segment, click that construction type from the palette on the Editor toolbar and draw the curve on the map. You can even switch among construction types after each segment, allowing you to build the exact shape you want. For example, if you are drawing a road with a bend in it, you may want some of it to be straight and some to be curved. To do this, start with Straight Segment, digitize the straight segment, then click a curved segment construction method and create the curve.
You digitize a new line or polygon feature's shape by drawing an edit sketch, which is the underlying representation of the feature's geometry. As you sketch, you see a WYSIWYG preview with the actual symbology used for that template, with vertices symbolized as green and red squares.
A sketch is composed of all the vertices and segments of the feature. Vertices are the points at which the sketch changes direction, such as corners; segments are the lines that connect the vertices.
Snapping allows you to create features that connect to each other so that your edits are more accurate and have fewer errors. With snapping, your pointer will jump, or snap to, edges, vertices, and other geometric elements when it nears them. This enables you to position a feature easily in relation to the locations of other features. As you move your pointer around the map, it snaps automatically to points, endpoints, vertices, and edges. All the settings you need to work with snapping are located on the Snapping toolbar, including enabling and disabling snapping types and setting snapping options. The main snap types are buttons on the toolbar, but additional ones are available on the Snapping menu.
A SnapTip is a small piece of text that pops up to indicate the layer you are snapped to and with which snap type (edge, end, vertex, and so on). You can set the text symbol (font, color, size, and so on) for SnapTips and whether the text includes the layer name, snap agent type, or both.
The snapping tolerance is the distance within which the pointer or a feature snaps to another location. If the element being snapped to—such as a vertex or edge—is within the distance you set, the pointer automatically snaps to the location. You set the default snap tolerance value in pixels.