when I use osclasswizard theme, I see the code related to the location drop down select, in js / main.js file as follows:
$("#sCountry").on("change",function(){var e=$("#sRegionSelect").text(),i=$("#sCitySelect").text();$("#sRegion").next().children(".select-box-label").text(e),$("#sCity").next().children(".select-box-label").text(i);var t=$(this).val(),s=osclasswizards.base_url+"?page=ajax&action=regions&countryId="+t,o='<option value="" id="sRegionSelect">'+e+"</option>";""!=t&&$.ajax({type:"POST",url:s,dataType:"json",success:function(e){var i=e.length;if(i>0){for(key in e)o+='<option value="'+e[key].pk_i_id+'">'+e[key].s_name+"</option>";$("#sRegion").html(o)}}})}),$("#sRegion").on("change",function(){var e=$("#sCitySelect").text();$("#sCity").next().children(".select-box-label").text(e);var i=$(this).val(),t=osclasswizards.base_url+"?page=ajax&action=cities®ionId="+i,s='<option value="" id="sCitySelect">'+e+"</option>";""!=i&&$.ajax({type:"POST",url:t,dataType:"json",success:function(e){var i=e.length;if(i>0){for(key in e)s+='<option value="'+e[key].s_name+'">'+e[key].s_name+"</option>";$("#sCity").empty().html(s)}}})}),
looks like the following url post is the most decisive,
s=osclasswizards.base_url+"?page=ajax&action=regions&countryId="+t,o='<option value="" id="sRegionSelect">'+e+"</option>";""!=t&&$.ajax({type:"POST",url:s,dataType:"json",success:function(e){var i=e.length;if(i>0){for(key in e)o+='<option value="'+e[key].pk_i_id+'">'+e[key].s_name+"</option>";
AND
t=osclasswizards.base_url+"?page=ajax&action=cities®ionId="+i,s='<option value="" id="sCitySelect">'+e+"</option>";""!=i&&$.ajax({type:"POST",url:t,dataType:"json",success:function(e){var i=e.length;
where the destination file processing ?
so that only displays the dropdown location if has ad/item