A federal board Thursday approved the renaming of 16 sites in Texas whose names include the word “Negro,” a change long sought by politicians and activists in the state, but one that will affect only a small fraction of the hundreds of racist names of towns and geographical features that remain in the United States. The U.S. Board on Geographic Names, a committee of the Department of the Interior, signed off on the name changes weeks after lawmakers in Texas unanimously passed a bill urging the board to approve them.