The lower planetary systems, up to the limit of the earthly stratum, are said to be situated in His legs. The middle planetary systems, beginning from Bhuvarloka, are situated in His navel. And the still higher planetary systems, occupied by the demigods and highly cultured sages and saints, are situated in the chest of the Supreme Lord.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
भूर्लोकः कल्पितः पद्भ्यां भुवर्लोकोऽस्य नाभितः । हृदा स्वर्लोक उरसा महर्लोको महात्मनः
bhūrlokaḥ kalpitaḥ padbhyāṃ bhuvarloko'sya nābhitaḥ | hṛdā svarloka urasā maharloko mahātmanaḥ
SB 2.5.38