A B717 flight crew deviated from their taxi clearance when they had trouble finding Spot 3 on the DTW commercial taxi chart.

Narrative

After the ground crew pushed us back from gate the aircraft was blocking the gate next to ours. An air carrier was going into that gate so we offered to move forward to accommodate them. Ramp control gave us taxi instructions to pull straight forward and taxi to Spot 3. After verifying where Spot 3 was; the Captain started to taxi. It appeared that the only way to get to Spot 3 was to taxi onto Kilo. The Captain and I figured that Spot 3 was on Kilo. However; when we got onto Kilo I called ground and told them we were on Kilo and that was when they told us that we were in violation of the FARS. The event occurred because the Captain and I were under the impression that ramp control wanted us to taxi down to the Spot 3 near the de-icing pad. Which is the de-icing pad Spot 3 not the Spot 3 where they wanted us to be. I realized after the fact that on the DTW commercial chart north ramp page that the Spot 3 we should have been going to was right on Echo. I think Spots 3; 4; 5; 6; should be depicted on the DTW airport chart instead of just being on the DTW north ramp page. The lines on Echo need to be painted better. The taxi instructions need to be more specific.