San Andreas Multiplayer (SA:MP) is a modification for Grand Theft Auto: San Andreas which turns it into a multiplayer game. You can play over the internet (or LAN) with up to 500 other people. You need the original Grand Theft Auto: San Andreas PC game to play San Andreas Multiplayer.
In SA:MP you are able to do almost anything that you can do in single player GTA. SA:MP also features the ability to create your own scripted game modes. There are many game modes that feature a series of different and fun things to do. Many of which are not possible in single player. There is many way's to script and mapp By Compiling. About your question: It should be pretty simple actually.
All you need is an updating timer (or OnPlayerUpdate) to get the player's distance to the point, then take the percent of that distance, and update the textdraw each percent (or each 5th percent, 10th etc..)
So let's say the distance is 100 yards (easiest example)
You run 10 yards, and that spot for where are you now moves one "spot" to the right.
You could use GetPlayerDistanceToPoint to make this work easily.