Google Earth is excellent application for quickly browsing data in KML files. However, if you have dataset with many placemarks, it might become a bit laggy. Below we will show how to solve this problem. As an example of data, we will use KML file with more than 64000 placemarks, collected from migrating Montagu's Harrier. 

Our KML file has around 57 megabytes:

After we open it, Google Earth shows correct content, but it becomes a bit unresponsive. Moving current view takes around 30 seconds, because apparently Google Earth is not used to presenting so many placemarks at the same time:

To solve this and be able to quickly move over the globe, we need to temporarily disable drawing placemarks and draw path only:

When drawing path only, our window will look like this - and you will be able to move over the globe freely, without any lagging/delays:

 

Now, when you will be interested in placemarks in some area, please do as following:

1. Zoom in to the area of interest.

2. Check "Placemarks" checkbox when being zoomed in to the area of interest (the same checkbox we unchecked in above steps).

3. You will see placemarks and google earth won't be lagging when drawing only subset of all placemarks:

That's all, thank you for reading. If you would have any questions, please contact us.