title: Shapefile to Topojson conversion
body: <p>I am trying to convert the Ghana admin1 shapefile that can be found <a href="http://biogeo.ucdavis.edu/data/gadm2/shp/GHA_adm.zip" rel="nofollow noreferrer">here</a>. My end goal is to obtain a TopoJSON as described in this <a href="https://stackoverflow.com/questions/16925131/shapefile-to-topojson-conversion-problems">question</a>.
  I have used this command on a Linux machine:</p>
  
  <pre><code>ogr2ogr -f GeoJSON GHA_adm1.json GHA_adm1.shp
  </code></pre>
  
  <p>And it returns this:</p>
  
  <pre><code>Unable to open datasource `GHA_adm1.shp' with the following drivers.
  ... here goes a long list of drivers...
  </code></pre>
  
  <p>I am I doing something wrong? Should I install other "drivers"? But how? Thanks.</p>