Wireless Sensor Networks (WSNs) are a common place nowadays. These networks consist of a huge number of small, low power and cheap commodities, capable of sensing, processing and communicating with each other to carry out the required task(s). WSNs have many emerging and attracting applications with wide deployment in both military and commercial sectors; however, it is not a fully mature field yet, so research is continue on numerous topics. Some open research issues of WSNs include localization, routing protocols, topology control, design of middleware architectures, development of new simulation and debugging tools, etc. In this paper, we are presenting a comprehensive survey on three main issues of WSNs, which include localization, routing and data gathering. Additionally, we have also highlighted a key problem in the research of localizati on in WSNs along with a theoretical model as its solution.