Population as per latest census which was held in 2017. But there can be few other factors as well as not all constituencies have same population, it will also depend on district population.
It don't make any sense. I am from tehsil kahuta and Kahuta tehsil should have at least one constituency instead of three or four tehsil making only one seat for national assembly..
Look difference between Rawalpindi 1 and others
New National Assembly Halqas 2018 (Total 7)
NA-57 Rawalpindi-I
(a) Kotli Satian Tehsil;
(b) Murree Tehsil; (c) Kahuta Tehsil, (d) Kallar Sayyedan Tehsil excluding Choha Khalsa Qanungo Halqa; and (e) Sagri Qanungo Halqa of Rawalpindi Tehsil of Rawalpindi District.
NA-58 Rawalpindi-II
(a) Gujjar Khan Tehsil; and (b) Choha Khalsa Qanungo Halqa of Kallar Sayyedan Tehsil of Rawalpindi District.
NA-59 Rawalpindi-III
(a) The following Qanungo Halqas of Rawalpindi Tehsil: (i) Adwal; (ii) Banda; (iii) Bassali; (iv) Chakri; (v) Gorakhpur; (vi) Sehal; and (vii) Rawalpindi. (b) The following Patwar Circles of Chaklala Qanungo Halqa: (I) Jarahi; (ii) Morgah; (iii) Topi, (iv) Lakhan-I: (v) Lakhan- II; (vi) Kotha KaIan: (vii) Dharnial; and (viii) Dhamman Syedan. of Rawalpindi District.
NA-60 Rawalpindi-IV
(a) Chaklala Cantonment except Census Charges No. 4, 5 and 6,
(b) The following Census Charges of Municipal Corporation Rawalpindi: (i) Charge No. 19: (ii) Charge No. 21, (iii) Charge No. 25: (iv) Charge No. 26; (v) Charge No. 27; and (vi) Charge No. 28. (c) The following Patwar Circles of Chaklala Qanungo Nalco, Chaklala-I; and (ii) Chaklala-II of Rawalpindi District.
NA-61 Rawalpindi-V
(a) Rawalpindi Cantonment;
(b) The following Census Charges of Chaklala Cantonment: Charge No. 4; Charge No. 5; and Charge No. 6 of Rawalpindi District.
NA-62 Rawalpindi-VI
The following Census Charges of Municipal Corporation Rawalpindi:
(i) Charge No. 11: (ii) Charge No. 12; (iii) Charge No. 13: (iv) Charge No. 14; (v) Charge No. 15; (vi) Charge No. 16; (vii) Charge No. 17; (viii) Charge No. 18; (ix) Charge No. 20; (x) Charge No. 22; (xi) Charge No. 23; and (xii) Charge No. 24 of Rawalpindi District.
NA-63 Rawalpindi-VII
(a) Taxila Tehsil; and
(b) Adyala Qanungo Halqa of Rawalpindi Tehsil of Rawalpindi District.