real-time tracker ,real time data get

I have a web page with PHP and JavaScript that contains a Google map. I need to see the change in the map marker, which moves according to the data given by Database i need to get the data from database periodicly without reloading the page, the data is the coordinates of the location of several people ,i have aleady the web page that shows the live locations to sevral people but i have to make a periodic refresh to the whole page to reload it and see the change of locations which is not practical