Free Quantum GIS Add ons for Creating and Editing Polygons
The QGIS provides a number of plugins when you are working with polygons. Some of the common plugins allow you to count the number of vertices of simple and multi part geometry, calculate the azimuths and distances of selected feature and figures and also the convergence factor, calculate the total sum of all the line lengths of each polygon, calculate the distance between the various vertices of a polygon and display it in the form for square or distance matrices, count and display the number of unique points that appear in a polygon vector layer and list the unique values that are present in an input vector field.
Some other functions that are added by the relevant plugins are computing the basic statistics like the mean, media, mode, standard deviation and sum of an input vector, locate and display the distinct points of intersection and view the results in a shape file, compute the normal or weighted mean center of the entire vector layer or the diagrams, compute all the statistics in order to assess the level of clustering around a single point or a group of points and perform several functions like union and intersection upon the vector layers. Some of these plugins also allow highlighting of features in the figures based upon some pre given conditions and creating buffers beside the figures. BestPlugins allows users to get the best QGIS polygon plugins which can be highly useful in redefining the way they deal with polygons.