Quick message...
First, I have made it so that labels for POIs are not displayed if zoom level is smaller than 13: POIs are too close to each other, the labels become a useless mess, and besides, when the map is zoomed out enough, locations (continents, countries, et cetera) can be recognized without any labels at all. Though, '13' should be replaced with an option to be set through user interface.
I am also creating an amusing kind of POI. If description of a POI matches 'airport', then, instead of the green translucent circle, an over-simplified image of airplane is drawn. And, an 'airport' doesn't have any label at all, no matter what zoom level: the number of airports is small enough than an airport doesn't need it.
And, the bright blue dot is replaced with a changing-colour one: bright green if GPS isn't available, yellow if GPS gives large speed and large distance till the point, red if the speed is large and distance is small, green if the speed is small and distance is large, black if both speed and distance are small. Speed is compared to pedestrian's 5km/h, and distance is compared to one hour of travel at current speed.
By the way, is it true that POIs are drawn even when they are outside the screen? It can make drawing work for cairo context about ten-twenty-forty times larger.
I'm still wavering: to install CSSU or not... Thank you for ModRana.