But one cannot tap rent where there is none. Taxes on other bases simply abort the taxed input or activity at the no-rent margins of land use, both extensive and intensive. This excess burden in turn puts an upper limit on the possible tax rate, thus sparing much rent from being taxed at all while destroying other rent completely. The only way to tap much rent is to tax land directly. From this it follows that efficiency does not require equal tax rates on the two, but only uniformity within each class.
Uniformity is impossible with capital because of differential concealability.
But land is uniformly non-concealable. The case for neutrality of land taxes is stronger under uniformity, but mainly requires that the tax not be a function of use. A land tax may be based on the current potential rent, or on value. In most countries other than Britain it is the latter. Values are not simply proportional to rents because many land values are elevated above that by expected higher future rents.