Carriers like Telstra and Optus use network engineering programs such as AToll and RFMap2 to plan out each cell tower, or 'node', as part of the larger 'mesh' network of towers. Radio Propagation modelling is used to determine the optimal location for each cell tower based on the area it must cover. However because each new cell tower interferes with all the surrounding towers, it must be positioned in a spot that covers an area the best it can without causing radio interference with another tower.
Radio interference and coverage area can be optimised by raising or lowering the antenna height, mechanically tilting the antennas down (to create a micro cell - ie. increase capacity) or up (to increase coverage area or reduce the impact of terrain).
Programs like AToll assist in the decision making process by factoring in terrain and other geographic disturbances to locate a position for the tower that optimises coverage area, reduces black-spots, and minimises interference. Other factors that come in to play are cost minimisation, access to backhaul networks, and aesthetics. Expenditure costs are often reduced by locating cell antennas on top of tall buildings, light poles, power lines, just about any tall object you can imagine. Viability is also assessed by modelling income generated, where income is a result of number of customers serviced. This is important to justify the $150,000 (avg.) capital outlay required to construct the site. Aesthetics is also important in metro areas where conventional monopoles are considered an eyesore, sites where antennas are hidden or painted to blend in are often called 'stealth' sites.