Snapping
SeaSketch drawing tools enable users to "snap" their sketches to vector data layers and other sketches while drawing. Holding down the CMD-key (or CTRL on Windows) while hovering the cursor near other features enables tracing of the edge of one shape to another.
Enabling Snapping in a Project
All SeaSketch projects support snapping but not all data layers do. For a data layer to be used in snapping they must be either an Esri Feature Service or Feature Layer. These types of layers serve vector data to the client that can then be queried for use in snapping. Image-based layers such as basemaps and Dynamic and Tiled Map Services do not support snapping.
If there is a particular layer that your users will find commonly useful for snapping we recommend adding it as a Guide Layer using the Sketch Class admin tool. This way the layer will be automatically turned on for visualization and snapping by default when digitizing that particular Sketch Class.