There are three kinds of Ihram for Hajj:
In Ihram of Qiraan, one intention is made for Umrah and Hajj together and the pilgrim does not relieved from Ihram after performing Umrah. The pilgrim is only relieved after having completing the rituals of Hajj.
In Ihram of Tamattu, first intention is made for Umrah and the pilgrim is relieved from Ihram after completing the rituals of Umrah and then a new Ihram is worn with the intention of Hajj within the months of Hajj of same year.
In Ihram of Ifraad, one makes intention of Hajj only during the days of Hajj.
From above description it is understood that he who is making Hajj of Qiraan will be wearing his Ihraam from the Miqaat and all the Miqaats are outside of the boundary of Haram.
Those who are making the Hajj of Ifraad should wear their Ihraam from Masjid-ul Haram or anywhere within the boundary of Haram. Those making the Ihraam of Hajj-e Tamattu, if they are already within the boundary of Haram then they should put on their Ihram from Masjid-ul Haram or anywhere within the boundary of Haram. If they are outside the boundary of Miqaat then they should put on their Ihraam from their respective Miqaat.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America
فاذا كان يوم التروية أحرم بالحج من المسجد. والشرط أن يحرم من الحرم أما المسجد فليس بلازم كذا فى الهداية
(الفتاوى الهندية ج١ص٢٦٣)