AutoTrace is a plugin for QGIS that allows you to trace existing features.
The AutoTrace plugin is based on the traceDigitize plugin by Cédric Möri and others.
Installation
AutoTrace is available from the official QGIS plugin repository. To install the AutoTrace plugin in in QGIS, simply select Plugins > Manage and Install Plugins… from the main menu. The Plugin Manager dialog will appear. In its left-hand panel, select Get more. Within the Search box now type autotrace. Select the AutoTrace plugin from the list and click Install plugin.
Using AutoTrace
To use AutoTrace, you need to first load layer(s) that you’d like to trace. With some layers are loaded, you will need to set sensible snapping options. In QGIS, from the main menu, select Settings > Snapping Options. Within the Snapping options dialog, select the layer(s) you wish to trace and set appropriate snapping settings (we recommend a 10-20 pixel tolerance, snapping to vertices).
Now add or create the layer you wish to digitize new features into.
To start tracing, first make your layer editable by right-clicking and selecting Toggle Editing. Select the AutoTrace tool from the digitizing toolbar. In order to follow (or trace) an existing feature, you first need to snap a new vertex onto an existing feature. With a new vertex snapped to an existing feature, you can simply:
- Trace along features by holding the SHIFT key.
- Trace the longest route (as opposed to the shortest) around polygons by holding both the CTRL+SHIFT keys.
Right-click to finish digitizing.
Download AutoTrace Plugin for QGIS
Watch the video on How to AutoTrace Plugin for QGIS
Source: Lutra Consulting