Creating polygons that share the boundaries of existing polygons

Question

I'm creating polygon (that about actual vegetation).

First, I create one polygon

After that, I will create more polygons that share the boundaries of existing polygon. But, it show result like below image.

How can I create polygons that share the boundaries of existing polygons.

And last, can I use trace method for creating polygon in QGIS?

Answer 1

In QGis 3.x

1. Enable the snapping toolbar and open snapping settings. Then, choose the advanced configuration and select your layer of interest
2. Go to Add Feature and start digitizing. When you will be close to a vertex, you should see a particular color
3. When you are done, I suggest you to check the topology

Answer 2

To create polygons that shares boundaries with existing ones,

In QGis 2.x

1. Settings > snapping options > choose advanced and select your layer. Then define the snapping mode, the tolerance and your units

2. Go to Add Feature and start digitizing. When you will be close to a vertex, you should see a particular color

3. When you are done, I suggest you to check the topology
4. As the trace method, you may see Freehand Editing useful

Answer 3

This digitising method might help:

1. Set Avoid Intersections ON as mentioned above.
2. Start digitising at a shared vertex or segment – digitise vertices that are not shared
3. Continue digitising
4. When you reach the last non-shared vertex – digitise a shared vertex
5. Then to finish digitise a last point – but make sure that it is located in a place that ensures the polygon extends over all shared vertices – right click to finish digitsing the polygon.

QGIS will create all the vertices for the new polygon as shown below [