> ## Documentation Index
> Fetch the complete documentation index at: https://webviewer-docs.mupdf.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Coordinate System

## Origin Point and Y-Axis

In **PDF**, traditionally the origin `(0, 0)` of a page is located at its **bottom-left point**. However, in **MuPDF WebViewer**, the origin `(0, 0)` of a page is located at its **top-left point** as this is more suited for web environments and digital displays.

<img src="https://mintcdn.com/artifex/P5Yywj_0Iti6e7Ik/images/coordinate-space.png?fit=max&auto=format&n=P5Yywj_0Iti6e7Ik&q=85&s=e773136e85b8ea1d24a4d54748f992be" alt="WebViewer Coordinate system" width="1700" height="880" data-path="images/coordinate-space.png" />

<Note>
  This is also known as User space versus Device space
</Note>

## Point Size

Coordinates are float numbers and measured in **points**, where:

* **one point equals 1/72 inches**.

Typical document page sizes are **ISO A4** and **Letter**. A **Letter** page has a size of **8.5 x 11 inches**, corresponding to **612 x 792 points**.

Now we know our document size the **MuPDF** coordinate system for the bottom right would be coordinate `(612, 792)`.

## Point Precision

Theoretically, there are **infinitely many** coordinate positions on a PDF page. In practice however, at most the first 5 decimal places are sufficient for a reasonable precision.