When discussing geography in Russian, you will frequently pair a generic geographical noun—like город (city) or река (river)—with a proper name.
An important stylistic rule is knowing whether the proper name declines alongside the generic noun, or if it stays permanently in the Nominative case.
Cities and Rivers (Agreement)
For well-known locations paired with terms like город (city) and река (river), the proper name generally declines to match the case of the generic noun.
| An hour later, the cartographer found the city of Moscow on this big globe. | Спустя час картограф нашёл город Москву на этом большом глобусе. |
Because найти (to find) requires the Accusative case, the inanimate noun город takes its Accusative form (which looks identical to the Nominative). To agree, the feminine proper name Москва takes its Accusative form, Москву.
| In our atlas, there is information both about the river Volga and about this continent. | В нашем атласе есть информация как о реке Волге, так и об этом материке. |
Here, both река and Волга take their Prepositional case endings (реке Волге) after the preposition о.
Lakes, Mountains, and Islands (No Agreement)
Different rules apply to geographical features like lakes (озеро), mountains (гора), and islands (остров). When paired with these generic terms, the proper name acts as a fixed label. It stays in the Nominative case, even while the generic noun declines.
| A year later, the scientists were again arguing both about the continent and about lake Baikal. | Спустя год учёные снова спорили как о материке, так и об озере Байкал. |
Notice how озеро correctly declines to озере in the Prepositional case, but Байкал remains unchanged.
| A year later, they checked the coordinates of Mount Elbrus and the island of Sakhalin. | Спустя год они проверили координаты горы Эльбрус и острова Сахалин. |
In this sentence, гора and остров are in the Genitive case to show possession ("coordinates of..."). However, their proper names—Эльбрус and Сахалин—do not decline.
Mixed Examples
When referencing multiple locations, you will often use both rules in the same sentence.
| A month later, we went from the river Volga to the island of Sakhalin. | Спустя месяц мы поехали от реки Волги к острову Сахалин. |
After the preposition от (from), Волга declines to match река in the Genitive case. But after к (toward), Сахалин ignores the Dative case of острову and stays firmly in the Nominative!