A small script that extract population and data from Wikipedia's list of biggest cities, it can be easily adapted for other pages and other informations.

extractdatafrombiggestcities in the world

// Run me in your console on http://en.wikipedia.org/wiki/List_of_cities_proper_by_population 

// from http://stackoverflow.com/questions/298750/how-do-i-select-text-nodes-with-jquery
var getTextNodesIn = function($el) {
    return $($el.find(":not(iframe)").addBack().contents().filter(function() {
        return this.nodeType == 3;
    }).get(0)).text();
};

var rowsSelector = '#bodyContent .sortable.wikitable.jquery-tablesorter tr',
  $rows = $(rowsSelector),
  cityPopSelector = 'td:eq(3)',
  cityCountrySelector = 'td:eq(7) a',
  citiesData = [];

$rows.each(function(_, item) {
  var $item = $(item),
    $pop = $item.find(cityPopSelector),
    pop = getTextNodesIn($pop).replace(/,/g, ''),
    validPop = !(typeof(pop) === 'undefined') && (pop !== ''); 
  if (!validPop) {
    return true;
  }
  
  var $country = $item.find(cityCountrySelector),
    country = $country.attr('title'),
    validCountry = !(typeof(country) === 'undefined') && (country !== ''); 

  if (!validCountry) {
    return true; 
  }
  
  var cityData = { 
    pop: pop,
    country: country
  };
  citiesData.push(cityData);  
});

console.log(citiesData);