Geometry Tools
Simplify geometry: Generalize lines or polygons with a modified Douglas-Peucker algorithm
Densify geometry: Densify lines or polygons by adding vertices
References and Resources
1. fTools Plugin
2. QGIS Basics
QGIS Simplify Geometry
The simplify geometry tool is a part of the fTools python plugin. The fTools function to
provide a one-stop resource for many common vector-based GIS tasks.
fTools is now automatically installed and enabled in new versions of QGIS, and as with all plugins, it can be disabled and enabled using the Plugin Manager. The fTools plugin adds a Vector menu to QGIS, providing functions ranging from Analysis and Research Tools to Geometry and Geoprocessing Tools, as well as several useful Data Management Tools.
How to Simplify Geometries
Go to the Vector menu -> Geometry tools -> Simplify geometries. This opens a window and your layer should be selected in the Input line or polygon layer drop down menu. It it's not, select it.
Next, look for the Simplify tolerance field. This measurement is in degrees so you want to use a really small number. The default of 0.0001 is a good place to start.
Check Save to a new file and create a new folder and a new file. Click OK. A new window will tell you how many vertices were removed. It should have removed somewhere between 70 percent to 90 percent of the original vertices. Close the window.
QGIS Densify Geometry
Densify Geometries in ftools adds the same number of nodes to all line segments