title: How to draw raster map in Python with a ESRI ASCII Raster format file like mapshow in Matlab?
body: <p>For example, I have a DEM file in ESRI ASCII Raster format like this:</p>
  
  <pre><code>ncols 480
  nrows 450
  xllcorner 378923
  yllcorner 4072345
  cellsize 30
  nodata_value -32768
  43 2 45 7 3 56 2 5 23 65 34 6 32 54 57 34 2 2 54 6 
  35 45 65 34 2 6 78 4 2 6 89 3 2 7 45 23 5 8 4 1 62 ...
  </code></pre>
  
  <p>I want to draw a raster map to display the topography. I know it can be achieved via mapshow in Matlab like</p>
  
  <pre><code>[Z,R] = arcgridread(filename);
  mapshow(Z,R,'DisplayType','Surface')
  </code></pre>
  
  <p>But how to do it in Python? And if the coordinate system is British National Grid, is it possible to add a shapefile layer (such as a polygon file) on the raster map in Python?</p>