This yantra is the Mahaganapati Yantra ( most divine one )and Ganesh has many different aspects 
              including Heramba,Haridra and Ucchishta Ganapati.
                       The tantrik compilation Sharadatilaka gives a most beautiful meditation on Mahaganapati (Arthur Avalon's
              English introduction): "...he is to be meditated upon as seated on a lotus consisting of the letters of the --
              alphabet. The sadhaka should meditate upon an island composed of nine gems, placed in an ocean of sugarcane
              juice; a soft gentle breeze blows over the island and makes the waves wash the shore thereof. 
                       The place is a forest of Mandara, Parijata and other Kalpa trees and creepers, and the light from the gems
              thereon casts a red glow on the ground. The sixaddening seasons are always there. The sun and moon brighten
              up the place. In the middle of the island is a Parijata tree

                       whereon are the nine gems and beneath it is the great Pitha (altar) on which is the lotus whereon is seated 
              Mahaganapati. His face is that of the great elephant with the moon on it. He is red and has three eyes. He is held
              in loving embrace by his beloved who is seated in his lap and has a lotus in her hand. In each of his ten hands he
              is holding a pomegranate, a mace, a bow, a trident, a discus, a lotus, a noose, a red water-lily, a sheaf of paddy 
              and his own tusk. He is holding a jewelled jar in his trunk. By the flapping of his ears, he is driving away the bees
              attracted to his temples by the fluid exuding therefrom and he is scattering gems from out of the jar held in his trunk.
              He is wearing a ruby-studded crown and is adorned with gem.

                   " Sharadatilakatantra, Agamanusandhana Samiti, 1933. 

                  This is the bija or root mantra of Ganesha, Gam.Before doing the puja, the sadhaka or sadhvini places this bija on
             his or her body, using the long vowels of Sanskrit. Ganesh is often pictured with the Hindu svastika (the word means 
             little picture of good fortune) and this is formed from four Gam bijas put together. 
                  Until the middle ages c.e., it appears that there was a separate cult of tantriks, the Ganapatyas, who followed 
             This Deva and his Shakti. Like Shiva, he was worshipped via a linga, but in this case red.