Gangadhar is called as Jatadhar for keeping hairs in the form of tresses. During the period of penances ascetics refrain from shaving and so the hairs stick to each other. This bunch of inter-locked hairs is called Jata. Jata is the symbol of Vanprastha (Third stage of life) and shaved head is the symbol of a Paramhamsa(final stage of life). Therefore Shiva is said to be Jatadhar because he is the spiritual master of ascetics. All the austerities are directed by Shiva alone. The regulative practices like observing fast, vows, meditation, sense-control, breath-control, listing Vedanta etc; all these paths of austerities for body, mind and intelligence are actually instructed by Shiva only. An erudite scholar of Puranas Acharya Bhaskar defines this name in the light of Puranas—

द्विविधतनुको दक्षध्वंसे बभूविथ यः पुरा
मृगमनुययावेकोऽन्यस्तु स्थितो मखमण्डपे।
अखिलसरितः परावारान् पवित्रतरान् धरान्
शिरसिकचतापन्नान् बिभ्रच्रु ्तोऽसि जटाधरः॥

At the time of destruction of fire-sacrifice of Daksha, you expanded yourself in two forms. You chased after the deer in one form, and from another expansion you became Jatadhari to give punishments. Oceans, rivers and mountains, all these are nothing but your hairs only. You hold all of them upon your head, so you are called Jatadhar. At the sacrificial ground you appeared in two forms— one was a hunter and other was the form of ascetic. Bhagwan Shankaracharya has recalled this form of primeval hunter in his Shivanand Lahri—
Deliberately Kapardi and Jatadhar, these two names of the Lord seems to be synonyms, but the first is a sign of neophyte stage and the later is a sign of perfection. Maintaining tolerance in all kind of calamities and engaging constantly in spiritual practices is the true form of worship of Jatadhar. For a sincere seeker of liberation, listening Vedanta by controlling the urges of body, mind and speech is the proper mode of worship of Jatadhar.