This page might also be called, "What a difference a hundred years can make." Helsinki has actually existed as a city since 1550, so for around 500 years. But it was only in the early part of the 19th century that it began to have any significance. This is owed to the Russians, who ruled Finland at the time after having won it from Sweden in 1809. Alexander the First moved the capital from Turku, on the west coast closest to Sweden proper to Helsinki, closer to Russia and St. Petersburg. (Aside, once Finland became independent Russia was not as happy to have it so close.)
The map on the left above shows what the southwest part of Helsinki looked like in 1893. At this time Finland was a part of Russia, but the ruling class in southern Finland was still Swedish, legacy of 600 years of occupation before 1809. (A legacy that still continues today.) For that reason, all the place names on the map are in Swedish.
The map on the right shows the same coast in 2013. Note the significant change in the coastline. Much of the water between the near islands in the west has been filled in by land reclamation efforts, some of which continue today. Even the three islands in the lower right of each map, situated off the Kaivopuisto Park area and more or less part of it, did not remain untouched.
My wife and I personally live in Ruoholahti, in an apartment on the spot marked by red dot on each map. Thank heavens for land reclamation! Most of the major filling-in of this area took place in the 1910's, ironically in the name of harbor construction. Unfortunately Ruoholahti itself - the name means "Grass Bay"; it used to be there marked as "Gräsviken" on the left - is gone without a trace, along with its southerly sister "Sand Bay". Only the name remains. The same can be said of the various islands: Kellosaari, Salmisaari, and Tammasaari, to name a few whose identity can only be found through seismic scanning for bedrock now. These have all been immortalized in street names though. Meanwhile appropriately enough our own street is named "Jaalaranta". "Ranta" being a beach, while jaala is a type of sailing vessel. We would have needed one of those to get to our home (or to be our home) in the old days in Ruoholahti.