Whether a tax is to be apportioned among the States according to the census taken pursuant to article I, section 2, or imposed uniformly throughout the United States depends upon its classification as direct or indirect.[251] The rule of uniformity for indirect taxes is easy to obey. It exacts only that the subject matter of a levy be taxed at the same rate wherever found in the United States; or, as it is sometimes phrased, the uniformity required is "geographical," not "intrinsic."[252] The clause accordingly places no obstacle in the way of legislative classification for the purpose of taxation, nor in the way of what is called progressive taxation.[253] A taxing statute does not fail of the prescribed uniformity because its operation and incidence may be affected by differences in State laws.[254] A federal estate tax law which permitted a deduction for a like tax paid to a State was not rendered invalid by the fact that one State levied no such tax.[255] The term "United States" in this clause refers only to the States of the Union, the District of Columbia, and incorporated territories. Congress is not bound by the rule of uniformity in framing tax measures for unincorporated territories.[256] Indeed, in Binns _v._ United States,[257] the Court sustained license taxes imposed by Congress but applicable only in Alaska, where the proceeds, although paid into the general fund of the Treasury, did not in fact equal the total cost of maintaining the territorial government. PURPOSES OF TAXATION Regulation by Taxation