What is Snapping?

Snapping is used to create coincidence when editing features. The snapping process moves a vertex of one feature to a location on another feature when the mouse pointer comes within a specified distance called the snapping tolerance. For example, if you want to snap a power line to a utility pole and the snapping tolerance is set to 25 pixels, whenever the power line comes within a 25-pixel range of the pole, it will automatically snap to it. The snapping tolerance can be measured in either map units or pixels.

When the location being snapped to is within the snapping tolerance (dashed circle), the snapping location (blue dot) moves to the location being snapped to (orange point).

There are three types of snapping properties you can set: layer snapping, sketch snapping, and topology snapping.

With layer snapping, you can specify whether features will snap to vertices, edges, or endpoints for each layer. You can set layer snapping properties for all layers in your map, whether or not they are editable layers. The graphic below shows examples of vertex, edge, and endpoint snapping.

The three types of layer snapping.

Sketch snapping properties are relative only to vertices and segments in your current sketch, not to vertices and segments in other layers. You can specify that new segments snap to lines that are perpendicular to your last segment or that new vertices snap to existing vertices in your sketch.

The two types of sketch snapping.

Topology snapping properties are used to snap an element to a node in a topology. You'll learn more about topology in the next exercise.

Topology snapping.

You set snapping properties in the snapping environment window. In the top part of the window, the order of the layers determines the order in which snapping will occur. You can drag the layers up and down to reorder them. Sketch and topology snapping properties are set in the bottom part of the window. If you are using the ArcGIS Survey Analyst extension, you can also set snapping properties for survey points.

The snapping environment window.