The title is incorrect. It is only the downtown area that will be relocated, not the whole city. And it will be moved 2.5 km, not 9 km. The downtown area is currently geographically located on the west edge of the city, and will move to the east edge of the city, see the map in this article: http://ecosistemaurbano.org/english/ecosistema-urbano-prequa... I have no idea where the "9 km" claim comes from. It is not quoted in the article. This is possibly a mix-up with an unrelated city mentioned in the article (Newtok in Alaska) which is considering relocating "9 miles" away.

Edit: @troymc: the BBC article is likely incorrect. Notice it quotes no sources. Maybe it assumed the whole city will move. Or maybe it takes into account population growth from people moving from other cities to Kiruna, because of the mine's expansion and increased economic/job opportunities. Either way, it is pretty obvious from all the relocation maps you find online that only the western edge of the city will move. Even the rendering at the original article http://nextcity.org/images/made/2033_plan_1200_862.png shows that only the western edge will disappear (compare it with a Google Maps satellite view).