A Yantra is a symbolic diagrammatic representation of a Deity, or parts of human body, various aspects of life – both spiritual and material, the shad chakras, the nadi centers etc. Take the above Sri Yantra (Also called Shree Chakra) for example. It represents Devi Lalita Tripura Sundari or Kamakshi Devi or Shodasi Devi or Shakti. The outer 3 lines, called the 1st Avarana, represent her feet, the inside 8 petal lotus, called the 3rd Avarana, represents her nabhi or naval and so on. There are 28 Devies placed in specific places on the 3 lines – or her feet. The other Avaranas also have different Devies placed at different specific locations. While doing Tantrik worship, where each of these Devies are individually worshipped with mantras and by offering flowers or Akshintas etc., it is more convenient to worship a Yantra than a picture or an idol. The same is the case with Hanuman yantra, or Kubera yantra or Navagraha yantra etc. – with variations in deities, numbers, locations and beeja mantras etc.