दिक्पूर्वपदादसंज्ञायां ञः

The affix ञ comes in the remaining senses after a word preceded by another that signifies 'direction' provided the compound is not a name.
To a stem, whose first member is a word denoting direction, and which is not a Name, the affix ञ is added, forming the feminine in आ ॥ The word असंज्ञायाम् qualifies the 'base'. This debars अण् ॥ Thus पूर्वशाला + ञ = पौर्वशालः 6.4.148, 7.2.117 'who is in the eastern hall'. Similarly दाक्षिणशालः, आपरशालः ॥

Why do we say "when not a Name"? Observe, from the word पूर्वेषुकामशमी 2.1.50 we have पूर्वैषुकामशमः 7.3.14, The example illustrates how first a compound of Tatpurusha kind is formed by the words पुव + इषु-कामशामी; "Ishukamshami-in-the-East"; the whole being the name of the city. Then when the Taddhita affix is added to this word, the first vowel is not vriddhied, as is the general rule 7.2.117; but the first vowel of the second member of the compound is vriddhied, viz the letter इ of इषुकामशमी by rule 7.3.14. Similarly अपरैषुकामशमः "who is in Ishukamashami-in-the-West".

The word 'पद' is used in the sutra for the sake of percision, for had the sutra been दिक्पूर्वादसंज्ञायां, there would rise the doubt, whether the the word-form दिक् was meant, or words denoting दिक् were meant. In fact the स्वरूपविधि is debarred by the use of the word ॥ For had it meant दिक्; the rule would have applied to words like दिग्गजः &c.