# problems understanding accumulate field with edges

I understand this node setup here with points:

result:

so i get each point offsetted by 0.01 from the accumulate field.

if i now change point to edge, i get this, which i don't understand:

maybe some GN pro can enlighten me...

• Let me put it in your words: "pls provide blend file" ;-) (No, please don't, just kidding!) Dec 19, 2022 at 19:12
• I would say it is related to the fact that Accumulate Field creates the values in the Edge domain, but are queried by Set Position in the Point domain, and therefore are interpolated. Why do you set this to "Edge" at all, if you want to influence the positions of the points? What exactly is the goal? Dec 19, 2022 at 19:22
• no goal - just trying to understand things ;) - that makes sense! Thank you! Dec 19, 2022 at 19:35

Quellenform is, of course, right: Accumulate Field node is noting down the values for edges, but Set Position is evaluating them in the Point domain, so there is an interpolation going on. Since vertices can be connected to more than one edge, they acquire more values the more connected they are. Here's a setup with edge and vertex indices exposed so we can check how that interpolation is executed exactly:
Big black numbers are the edge indices, small red numbers are vertex indices. Spreadsheet on the left is showing the final Z values, and the spreadsheet on the right is showing the values accumulating on the edge domain (connected to a Viewer). I'm using the Trailing socket so edge indices and the accumulating values are directly correlated: Index 0 gets a value of $$0.00$$, Index 6 gets $$0.06$$ and so on...
Contrasting the numbers for a while makes the method obvious: every vertex gets a final value of all their neighbor edge values combined, divided by the number of total connections. Let's take a look at a random vertex; say, vertex Index 12 in the middle. It has $$4$$ edges connected to it, with values (again, in this instance, correlated with their index numbers) $$10, 30, 9,$$ and $$29$$. Add them all up: $$78$$. Divide that by the number of connections: $$78/4=19.5$$ We look at the left spreadsheet and see that indeed, vertex Index 12 has a Z value of $$0.195$$.