Filtering (or subsetting) creates a smaller charts database and is sometimes required when the size of the charts database is larger than the avionics can support. This is often true of worldwide charts subscriptions. The subsetting feature of JDM allows you to specify your own filters based on airport, geographical region or runway length to accommodate your specific operational needs.

JDM does this by creating a special tailored region, adding all of the charts you specified in the filters to this new custom region. JDM then picks one of your existing regions "Canada and Alaska" for example, as the name of this region.

This might make it look as though the other regions have been dropped from the database, but in actuality, this is a custom database including all of the airports you have selected.

You can can confirm this simply by entering your flight plan and ensuring the charts that you expect to see are in the database.

Example
You subscribe to the following charts regions:

• Full USA
• Canada and Alaska
• Latin America
• Europe
• Atlantic Special Supplement

You then create a filtered subset of charts that only includes airports that have runway lengths greater than 3,000 feet.

When you download the database into the aircraft and examine the Chart Subscription page, you will only see a single region listed (e.g. Full USA), even though airports from all of your regions are included.