Tokio;122344;2334.6;...
Paris;3456782;1234.7;...

public class City
{
    public string Name { get; set; }
    public string Population { get; set; }
    public string Area { get; set; }
}

public class MyViewModel
{
    public IEnumerable<SelectListItem> Cities { get; set; }
    public string SelectedID { get; set; }        
}

public ActionResult Index(/*ViewModel.MyViewModel myViewModel*/ ???)
{
    myViewModel = new ViewModel.MyViewModel();            
    myViewModel.Cities = new SelectList(GetDataFromCSV(), null /* ??? */, "Name");
    return View(myViewModel);
}

protected List<Models.City> GetDataFromCSV()
{
    var result = new List<Models.City>();
    // Server.MapPath("~/App_Data/Cities.csv"
    ...
}

[HttpGet]
public JsonResult GetData()
{
    string data = // ??? (myViewModel.SelectedID etc);
    return Json(data, JsonRequestBehavior.AllowGet);
}

@model MyWebApp.ViewModel.MyViewModel
@Html.DropDownList("MyDropDown", Model.Cities, "--Select--")

<script type='text/javascript'>
    $(document).ready(function () {
        $("#MyDropDown").change(function () {
            $.ajax({
                url: "GetData",
                type: 'GET',
                success: function (result) {
                    $("#div1").html(result);
                    }
                });
            });
        });
</script>

private List<Cities> _data;

public ActionResult Index()
{
    myViewModel = new ViewModel.MyViewModel();            
    _data = GetDataFromCSV();
    myViewModel.Cities = new SelectList(_data, null, "Name");
    return View(myViewModel);
}

[HttpGet]
public JsonResult GetData(string selected)
{
    // selected = Имя выбранного элемента (то есть название города)
    var d = _data.Where(x => x.Name == selected);
    return Json(JsonConvert.SerializeObject(new { name = d.Name, area = d.Area, population = x.Population }), JsonRequestBehavior.AllowGet);
}