title: Find size of polygon area in Tkinter Canvas, Python
body: <p>I am creating program that analises areas of user-drawn shapes.
  Here is sample of code that creates polygon from dots. Program gets dots from mouse motion. Firstly it draws lines, than erases them and draws figure.</p>
  <pre><code>def finish_custom_selection(self, event):
      # self.custom_lines_id - list of id of created by mouse motion lines [id1, id2 ...]
      # self.canvas_for_selection - tkinter canvas I work with
      # self.custom_dots - list of dots coords pairs [(x1, y1), (x2, y2) ...]
      
      for line in self.custom_lines_id:
          self.canvas_for_selection.delete(line)
  
      item = self.canvas_for_selection.create_polygon(*self.custom_dots,
                                                      dash=(10, 10), width=2,
                                                      fill='',
                                                      tags=&quot;draggable&quot;,
                                                      outline=&quot;blue&quot;)
  
      self.custom_dots.clear()
      self.custom_lines_id.clear()
  </code></pre>
  <p>So here is my question. How can I calculate size of this polygon area? I know algorithms only for convex polygon, but these area can be completely random. Maybe there are any built-in method I am missing?</p>