Working with Data with the MapPoint Web Service Find APIs - Querying for Geographic Extent for a Data Source
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Now that you know how the country/region information is organized in MapPoint Web Service, let’s look at how to get a list of countries supported by different data sources.
The geographic extent of the countries supported by a particular data source is defined using theEntityExtentfield of theDataSourceobject. TheDataSource.EntityExtentfield is an array of integers that represent the corresponding country entity IDs. The following code snippet shows how to get the geographic extent of the data sourceMapPoint.NA:
//Create Common Service SOAP Class instance
CommonServiceSoap commonsoap = new CommonServiceSoap();
//Assign credentials
. . .
//Get Data Source Info for MapPoint.NA
DataSource[] datasources =
commonsoap.GetDataSourceInfo(new string[] {"MapPoint.NA"});
//Get entity extent
int[] extents = datasources[0].EntityExtent;
The geographic extent is expressed using the country/region entity IDs discussed in the previous section. To get the name of the country that each entity ID corresponds to, call the CommonServiceSoap.GetCountryRegionInfo method.
Programmatically Mapping a Country/Region to a Data Source
So far, I have shown how to get supported countries given a MapPoint Web Service data source. A common application scenario would be the other way around: choosing an appropriate data source for a given country. To programmatically map a country/region to a data source, you need to identify the task for which you need the data source, deciding whether you want a data source to find a place, find an address, calculate a route, or render a map. You can use the DataSourceCapabilityenumeration discussed in Chapter 5. Once you have theDataSourceCapabilityfigured out, you can get an appropriate MapPoint Web Service data source name using the following code:
private string[] GetDataSources(string countryRegionName,
DataSourceCapability capability)
{
if(countryRegionName == null || countryRegionName.Length <= 0)
throw new Exception(
"Invalid country/region name; country/region
name cannot be null or empty.");
ArrayList datasourceList = new ArrayList();
//Now loop through the list of data sources and
//see what data source fits the purpose
foreach(DataSource datasource in datasources)
{
if(((int)datasource.Capability & (int)capability) != 0)
{
//OK, this data source has the capability, but does it support the
//entity extent (the country that we need a data source for?)
int[] entityextent = datasource.EntityExtent;
//Now loop through each entity extent and compare the input name
foreach(int entityid in entityextent)
{
//Now look up using the entity id to see if the input
//country/region name matches any entity extent
//in this case I'm country region information
//cached in a Hastable
if(this.countryRegionsTable[entityid] as string
== countryRegionName.Trim())
{
//Found a match for both requirements
//Return the name
datasourceList.Add(datasource.Name);
break;
}
}
}
}
if(datasourceList.Count <= 0)
throw new Exception(
"No data source found to match your needs for this country.");
//Return a sorted list
datasourceList.Sort();
return datasourceList.ToArray(typeof(String)) as string[];
}
The previous function returns an array of suitable MapPoint Web Service data source names. ThecountryRegionsTableis aHashtable containing cached country/region information indexed on the entity IDs. Thealgorithmused in this function is pretty simple: first, find a data source with matching capability, and then get the geographic extent for that data source and see whether there is a match with the input country/region name. You can also find the code for this function, along with other functionalities discussed in this section, in the Chapter 6 solutions on the companion material.
With this introduction to find methods, entity types, and data source relationships, let’s look at how to perform various spatial queries using Find Service.
Next: Working with Find Methods >>
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 This article is excerpted from chapter six of the book Programming MapPoint in .NET, written by Chandu Thota (O'Reilly; ISBN: 0596009062). Check it out today at your favorite bookstore. Buy this book now.
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