Cuente y muestre cuántos resultados de columnas específicas

Aquí tienes:-

$query = $this->db->query('SELECT city, COUNT(city) AS jobcount FROM `jobs` GROUP BY city ORDER BY jobcount DESC');

if ($query->num_rows() > 0)
    foreach ($query->result() as $row) 
        $data[] = array(
            'total' => $row->jobcount,
            'city'  => $row->city
        );

return $data;

No olvides intercambiar 'jobs' con el nombre de tu mesa