platformer collision detection trouble

i'm trying to make a sonic clone but i can't seem to figure out how to do the collision detection. how do you check collisions with a platformer game. any help appreciated.

There are a couple of ways to do this with a Tile-based game like Sonic:

a) Check the player sprite against the surrounding tiles

b) Check the player sprite against a collision map

Have a look through the code archives, there are a number of useful articles and code snippets.

i know how to make and use a map editor but i can't seem to figure out how to deal with the collision tiles. i looked in the code archives but my question remains unanswered

Here's a good starting point:

http://www.blitzcoder.com/cgi-bin/articles/show_article.pl?f=gamekrylar01282001.html

thanks.

I drew it first, test collision move based on speed (ie sloowdown gravity) draw again, test again. Then Clear screen, and with retro clones it's okay to be slow. In fact almost better.