Almost everyone has done a jigsaw puzzle but the strategies for solving small puzzles don't work very well on a large puzzle. The largest puzzle I've ever done is 5000 pieces. Frankly that's too big. You need a large work space. I had to do it on the floor.
My favorite size is 1500-2000. You can solve these puzzles by hunting and pecking but most people find that gets tedious fast and can take a lot of space. You need to have a plan.
I like to divide and conquer, making this a suitable post for my tech blog.
The puzzle I'm using for this post is one I picked up recently at a thrift shop. I've never done it before. It might have missing/damaged pieces. This post is a stepwise breakdown of the build. None of the images were set up. This is exactly how I do a build.
This puzzle has four main areas: sky, water, boats/houses and trees. It is a difficult puzzle because both the water and sky areas are sizable and the boats and trees lack large features - a piece of boat, house or trees could go in several different areas.
This puzzle needs a divide and conquer strategy. Imagine a scenario where someone gave you just the pieces of the stern of the "Adler" boat prominent in the foreground. That's a much simpler problem. Most people would have no problem putting that together. That's the value of divide and conquer, breaking a big problem up into smaller problems.
The first and ongoing task in my approach is separating the pieces. I pluck pieces one by one from the box and sort them into piles. Some piles that I know I'm going to only tackle later don't need to be neat, face up - they could go in a bowl, e.g. the water.
I start by scanning the box. Usually something stands out visually. I sort these first - they are the easiest to see. The sky includes a lot of pieces that contain bits of mast, trees, etc. I want all pieces that contain any sky. The interfaces between the sky and other objects can be one of the easiest parts of the puzzle to tackle. For now I sort them all into one pile.
Part of the water contains reflections. For now all I want are the featureless water pieces. Some of the reflections might be hard to tell apart from other dark areas of the puzzle.
While sorting, other things begin to stand out: the red ball, the green house, wording on the boats, the yellow mast with the green rope, the blue rope. These features have relatively small numbers of pieces and I assembled some of the them while I was sorting.
As sorting continues, I start to notice the trees and white pieces. These go in more piles. Edge pieces go in a pile. Here are pictures of my first sort. When I stop easily finding pieces for any of these piles, I stop.
There's a lot left in the box at this point but I can start putting the puzzle together. Obsessing on getting all of any pile is inefficient. Alternating between sorting and assembling will tune your eye.
For example, with the first sort, I was able to assemble most of the red ball, the red car, the green house and some of the boat hulls at the water line.
Then I scanned the box and found a few more pieces with red. Every time I look in the box for a certain kind of piece I continue to look for pieces that go in all of the other piles. So, over time, each pile becomes more complete.
Now that my eye is tuned into the red, particularly, the water with red reflections, I am more likely to notice them in the box. I don't need to focus on finding them all now. My eye won't be able to help noticing them while I'm scanning the box later.
While sorting I noticed the blue line atop the stern of the foreground boat and the lettering below it and started pulling those. Sorting is a continuous process.
That's pretty much it for the low hanging fruit. Next I needed to decide which pile to start with.
Commonly people start with the edge pieces first. I usually don't. In a big puzzle, it doesn't help much. This puzzle is 52 x 39 (2028 pieces). The edge is 178 pieces, 8.8% of the puzzle.
Compare that to a 16 x 13, 208 piece puzzle where the edge is 54 pieces, 26% of the puzzle. You do the edge and your well on the way to done. But in the big puzzle:
- the edge is harder. Some pieces may fit in more than one place. With half the edge being sky and water it may be hard to notice errors.
- some edge pieces may still be in the box. Remember, we aren't obsessing about finding every kind of any piece. A single missing piece breaks the edge making assembly difficult.
- assembling the edge takes up a lot of space and cramps the work space.
- assembling the edge doesn't help with the rest of the puzzle. It will later but early on it doesn't.
I started with the white pieces pile and the small easy piles (green, red ropes, etc.). Some of the edge pieces obviously fit with these so I pulled them from the edge pile.
I considered looking for more white pieces but those pieces are hard to place. They are interspersed with a lot of other pieces. I thought about the trees but they would be a lot easier after the houses/sky are done and create a context for them. So I started with they sky - the sky pieces that interface with the tree line, masts, etc. I first separated the plain old sky pieces from the ones I was interested in.
The plain old sky is a challenge but the masts, etc. were surprisingly easy. because the sky is so easy to spot in the box, I was pretty sure at this point that I had most of these pieces. Above is my first pass (yes, its upside down - that was my working perspective).
Notice that I pulled the relevant pieces from the edge pile. I was happy with how easy it was to assemble masts so I started pulling the large yellow mast pieces (left side of picture). Finished it looked like this:
Next i did the yellow masts, more of the white pieces and roof pieces.
Then a reorg of these three main puzzle areas to put them together. Since I'm working in a space barely bigger than the puzzle, I need to shuffle the work space around.
Now its pretty easy to place the rest of my white, roof and tree piles.
Now you can see the bottom of the box.Mostly water and dark pieces which I sort into three piles - dark pieces, water with reflections, remaining house, boat pieces.
These pieces are the dregs. They aren't easily identifiable as anything specific - they didn't fit in any of my previous piles. However, the houses, boats, trees, etc. went together pretty easily because the puzzle was mostly complete - I only had to scan the empty holes. There was one missing piece (in the trees, by the mast at the treeline). With a used puzzle you're never sure how many pieces will be missing. Another good reason not to obsess about finding every piece.
All that's left are the real dregs - the featureless dark pieces, sky and water. I retrieve the featureless sky and water pieces that I had previously set aside.
Finishing these featureless areas of a puzzle is an art of its own. It is too tedious for many people.
These puzzle pieces have subtle patterns in shape and I was able to separate them into horizontal and vertical pieces. Not 100% accurate but it divides the pool roughly in 2 piles. These pieces have some pretty unique shapes so many of these pieces could be matched by shape.
At this point some trial and error is unavoidable. These pieces have no useful features - no texture, color variation. Nothing. You need every trick you can find to reduce the number of pieces you need to try.
The left edge of the puzzle had a consistent cutting error so those pieces were easy to spot. Like I said, you need every trick you can find...
Here's the finished puzzle. In addition to the missing piece, there are two damaged pieces bottom left.
I believe the key is solidly in the sorting process. If i were to give someone the pile of pieces for any puzzle object they can probably assemble it.
If you can accurately distinguish pieces by color, texture, pattern you can divide and conquer. I'm able to sort quickly and accurately so I'm able to enjoy a puzzle that would otherwise boggle.
I've found that, like many problems in life, you can't tell exactly how you are going to solve a puzzle. It's a process, not an algorithm although individual steps may be algorithm-like. Sorting achieve two key results. It gives you a pile of pieces that comprise a thing (or at least similar/indistinguishable things). Some of these piles you want because they have structure that you can easily assemble. These you are going to build early. Others have no structure. These you are going to build last. After the shape of the rest of the puzzle is done and you have a clear area with all of the boundaries known - so you can rely on trial and error if you need to.
Perhaps the most important benefit of sorting is that every time you remove pieces of a clearly visible type from the box you make it possible to see other categories of pieces. In engineering terms you can think of it as removing noise. When you take all of the bright blue sky pieces out you can start to see more subtle patterns.
Sorting can also be recursive. Once you sort a pile you may notice that it contains a clear subdivision of pieces. Like I did with the sky - plain old sky and sky with masts, etc..
The eye is very good at seeing patterns I'm lazy so my approach lets my eyes do most of the work.
A final point I will emphasize is that this approach also doesn't need to be 100% accurate. A good sort is more efficient but a sloppy sort will still work. With practice the sorts will get better. It is actually critical to not agonize over the sorts or it will be no fun at all. And it's best not to obsess. With this strategy you don't need all of the pieces to start assembly. Stray pieces will stand out like a sore thumb. For instance, after you've removed the sky, a bright blue sky piece will jump out at you - and you'll know exactly which pile it goes in. Or, better yet, if it's a distinctive piece, where it goes in the puzzle.
