Wilfried, to draw custom symbols for my pushpins, I parse the information from the balloontext. There is also the number of pushpin as ID, which is on a hierachical manner. So it starts with 1 and than 2 and than........xxx. This means I can rearrange them and than skip some drawings right?

The only problem than is how to get the pushpins from the view? Suppose I've zoomed in a part of the map with only a part of all the pushpins in it. Than I need to get those pushpins within the map, is that possible?
You can calculate the coordinates of the 4 corners of the map, then check wich pushpins are in or out of view.

Also what is the relation between the altitude and the distance in meters on the map.
I dont know. I think best is to experiment a little with it to see the results.

is there a limitation of loading custom symbols? Cause I've about more than 200 symbols loaded, but suddenly it says "Failed to import".
I think I have seen posts of people loading more custom symbols. I dont think there is a limiation but I'm not sure.

could it be because everytime I load a custom symbol with the same name, mappoint gets so slow with loading custom symbols? That reminds me at the beginning when I loaded pushpins with the same name.
Yes this is quite good possible. I should give each one an exclusive name.

I know it's a lot of questions, but than I'm almost finished and overcome all the problems. Thank you.
It's ok