Converting cluster of Points to Polygons using QGIS
Convex hull - as mentioned by Kazuhito - is one option, but - depending on the cluster shape - you will get more appropriate polygons using concave hulls, for example implemented in ConcaveHull plugin.
You may be interested in Convex Hull which is in Processing | QGIS geoalgorithms | Vector geometry tools
. There is Field option which can be used with Method Create convex hulls based on field
.
Or from the menu Vector | Geoprocessing Tools | Convex Hull(s)
.
Many Thanks, Techie_Gus and underdark for information.