How can a tax be represented in a simple demand and supply diagram?

A tax can be indirect, imposed by the government on goods and services (e.g VAT) or direct (e.g. income tax). There are 2 types of indirect taxes: specific tax, which is a set amount and ad valorem, a percentage tax based on the value added by the producer (e.g. VAT). Note that governments prefer ad valorem taxes as it means the tax revenue will increase as the economy grows. The imposition of either type of tax has a similar effect as a rise in a firm's costs, therefore affecting a firm's supply curve. Non-price determinants like tax, cause the supply curve to shift upwards (to the left, as they are negative impacts) and not a movement along the curve. Before analyzing their impact, it is necessary to understand a supply-demand graph (shown image) and that in the supply curve, the price is directed related to the quantity demanded but, in the demand curve, these are inversely related. The intersection of these two curves, in a free market, gives rise to the market's equilibrium price and quantity. Because a specific tax is a constant value, the supply curve will shift to the left by the full amount of the tax (parallel). (show graph) Causing the equilibrium price to increase and the quantity to decrease. The same conclusion is arrived to with the ad valorem tax but this shift will not be parallel as the tax is a %. (show graph) Overall, both these taxes have similar impacts in a free market, however the way they are represented is different (as it can be seen from the graphs).