Map of Khurasan and other provinces governed by the Tahirids, circa 836 AD, based on information given by the geographer Ibn Khurradadhbih d. ca. 911 AD. He provides a list, pages 34-39, of the revenues of each province and district under the control of the Tahirids. Cities and towns in the provinces are derived from his itineraries, pp. 22-54. The works of Le Strange and Barthold were used to determine the locations of several of the lesser-known districts, especially those in Tukharistan.  
Background topography taken from DEMIS Mapserver, which are public domain.
Works Cited:

Barthold, W. Turkestan Down to the Mongol Invasion. 2nd Ed. London: E.J.W. Gibb Memorial Series, 1928.
Ibn Khurradadhbih, Abu al-Qasim 'Abd Allah. Kitab al-Masalik wa'l-Mamalik. Ed and trans. M.J. de Goeje. Leiden: E.J. Brill, 1889.
Le Strange, Guy. The Lands of the Eastern Caliphate: Mesopotamia, Persia, and Central Asia, from the Moslem conquest to the time of Timur. Cambridge: Cambridge University Press, 1905.
Own work
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