Here is how my final form looked after I added a world map picture and 2 new buttons:

The only new code I had to write was for the “Map It” button. I needed to access the selected row in the results table, grab the longitude and latitude, and add a point on the map at that location.

Here is how I did that:

private void btnMapIt_Click(object sender, EventArgs e)
{
  DataGridViewSelectedRowCollection rows = grdResults.SelectedRows;
  foreach (DataGridViewRow row in rows)
  {
    double longX = Convert.ToDouble(row.Cells["lng"].Value);
    double latY = Convert.ToDouble(row.Cells["lat"].Value);
    Point mapPoint = ConvertLatLon2ImagePosition(longX, latY);
    PlotPosition(mapPoint);
  }
}

The source code for the two functions, ConvertLatLon2ImagePosition and PlotPosition, was already covered in the WorldMapper post. The “Clear Map” button’s code is also found in that post.

In the above screenshot, I queried GeoNames for Toronto and was able to map the location of the city on the map. For non-US locations, be sure to look up the county code here.

This concludes our GeoNames posts for now. Many of these early projects are really laying the groundwork for some much cooler projects to come. If you have any questions about what we’ve already covered or have an idea for a project you would like to see, send us an e-mail.

A simple form can be set up to capture the necessary input parameters: location name, country, and the number of rows returned. At the bottom of the form, add a DataGridView control to display the XML results. My completed form looks like this:

Since we are going to be dealing with XML in our code, add this using statement to the code:

using System.Xml;

In this example, we only need to add code to the button to perform the search. Double-click on the button itself to create a Click event in the code view. Here is how I performed the search:

string searchPhrase = txtSearch.Text;
string searchCountry = txtCountry.Text;
int maxRows = 0;
try
{
  maxRows = Convert.ToInt16(txtMaxRows.Text);
}
catch
{
  MessageBox.Show("Enter a valid number of rows!");
}
if (maxRows > 0)
{
  string url = "http://ws.geonames.org/search?q=";
  url += searchPhrase + "&maxRows=" + maxRows.ToString() + "&country=" + searchCountry;
  lblURL.Text = url; 
 
  try
  {
    DataSet dsResults = new DataSet("xmlResults");
    dsResults.ReadXml(url);
    grdResults.DataSource = dsResults;
    grdResults.DataMember = "geoname";
  }
  catch
  {
    MessageBox.Show("Error in connection or URL!");
  }
}

In the above code, we perform several steps. We first capture and validate the input parameters from the form’s controls (txtSearch, txtCountry, txtMaxRows). We then construct the URL as we discussed in the previous post. Finally, we use the URL to perform the search and return the results in an XML dataset. The results are easily displayed in the DataGridView for display.

Here is what the results for an “Oakland” search looks like:

C# and the .NET framework provide easy access for obtaining and using XML data. As the above example shows, it makes no difference if the XML data is on your local hard drive or a website. Further processing of XML is also very straightforward and will be explored in future projects. For example, the GeoNames search results could be added onto a map or exported to a local file.

Continue to part 3

The Geonames web service accepts a query as a URL and returns an XML or JSON document. For example…

http://ws.geonames.org/search?q=detroit&maxRows=3

returns an XML document with the top 3 results for Detroit. As expected, the city of Detroit in the State of Michigan (USA) is returned first which is probably what the search was intended to find.

The query can be confined to a particular country like this…

http://ws.geonames.org/search?q=detroit&maxRows=3&country=US

Geonames offers a number of other web services, including recent earthquakes, weather conditions, and reverse geocoding. While we may explore these later, for now let’s focus on obtaining latitude and longitude information for places.

The results above are returned as XML in your web browser. This sort of display is fine for casual viewing but not for custom mapping applications. Fortunately, C# provides an easy framework for obtaining and working with XML documents.

Continue to part 2