You need t take a use of the Google Maps Script to load Google Maps V3 with Multiple Markers, first create custom database enter latitude and longi, in it and then call Google Maps Scripts in HTML/aspx markups
Now use ASP.Net Repeater Control to populate the markers array Thus when the page is rendered in the browser the values from database are loaded within the marker array.
see below sample for more details
http://www.aspsnippets.com/Articles/Show-Google-Maps-using-Latitude-and-Longitude-in-ASPNet.aspx
use below link for Google API
https://maps.googleapis.com/maps/api/js?key=AIzaSyC6v5-2uaq_wusHDktM9ILcqIrlPtnZgEk&sensor=false
check below link for more details
http://www.aspdotnet-suresh.com/2013/05/aspnet-show-multiple-markers-on-google.html
Thanks
Koolprasd2003
Editor, DotNetSpider MVM
Microsoft MVP 2014 [ASP.NET/IIS]