You mean Gaalackyo as one city including south Gaalkacyo, probably then it's larger than Bosaso.
As one city definitely but even without.
The density and width of Gaalkacyo are underestimated. The city is majority residential, houses upon houses into the distance. Bosasso is large due to the number of commercial spaces but people don't live in an office.
Apart from main road, kamaluudin, xero dayax and suuqa weyn, Nth Gaalkacyo is all houses.