Throttle http response (REST) Angular

Hi, this is basically a question. I have a service returning http response. it then plots markers on a map. at the moment everything appears at once, which I dont want. I want it to return the json response slowly document by document. I am prepared to pay $20 for the correct answer my current code is public ngOnInit() { [login to view URL] .getAdUnits() .subscribe(data => { [login to view URL](data); for (const key in data) { if (data[key]) { realTimedraw(data[key]); payCount(data[key]); [login to view URL](data[key]); } } });