"There is a map on the wall."
Translation:Hay un mapa en la pared.
The "rule" for "el arma" (instead of using "la" is not because the "ending in -ma". :-) All nouns beginning with A use "el" for the singular, regardless of whether the noun is masculine or feminine. Otherwise, the trailing A in "la" and beginning A in "alma" would not enunciate well and would sound like a single word. Using "el" instead of "la" puts the L sound between the two A sounds.
I probably did NOT explain that very well.