## 4.1 Coordinate system

Note that PDF documents use a different coordinate system than Hollywood. In the default coordinate system of PDF, shown below, the lower-left corner is at coordinates (0, 0), and the upper-right corner is at coordinates (width, height). The default resolution is 72dpi. In Hollywood the upper-left corner is at (0, 0).

An application can change the coordinate system by invoking page:Concat(). For example, if an application invokes `page:Concat(0.5, 0, 0, 0.5, 100, 100)` in the default state, the coordinate system shown above is transformed to the new system shown in the figure below:

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