A spark strip consists of several conductive objects in a row with a short gap in between, effectively forming a line of spark gaps. As with other spark gaps, the combined width of the gaps must be small enough for the ignition source to overcome.
There are several ways to achieve this:
scratched conductive film
By scratching thin lines across a conductive film (metallic paints, CDs) it is possible to get very large numbers of sparks out of a meager source. A more sophisticated method consists of etching a spark strip pattern in a printed circuit board.
Small pieces of wire, such as from a coathanger are glued to the wall. Gaps between each piece of wire cause a spark to be produced.
Veroboard is a ready-made circuit board with multiple copper strips or dots, a piece cut perpendicular to the copper strips will function as a spark strip.
Spark strips are sometimes seen as inferior to a screw based gap system, because they are often mounted on the wall of the chamber, as opposed to screws, where the spark is in the very centre of the chamber. This means that the flame from can only travel in one direction (away from the wall). A central gap allows the flame fron to spread in every direction towards the walls.