Strategy to solving/assembling high-number tile jigsaw puzzles - Case study: Eurographics 1000-piece 'Modern Locomotives' 19.25" tall x 26.625" wide

I was not able to find discussion on the topic, nor terminology; so at the risk of being presumptuous and redundant, I posit this otherwise rather nerdy post for those who may be interested in the mechanics of jigsaw puzzle solving. I apologize that I did not provide photographs of the puzzle in progress; rather, these photos are taken after completion and as such cannot convey the subtlety of the puzzle challenges. 

First, some key definitions and methodologies.

Parts of jigsaw puzzle per me:

1. The tesselated image: this may be any number of things, but the finer the detail of the image, tends to define a more challenging image. that said images that have have large areas of unvariegated texture or block color are the most challenging because they necessitate assemblage by 'brute force'.
2. Tesselations or Tile pieces consisting typically of curved and or flat edges, and 'plugs' and/or 'sockets' interlocking elements.
3. The 'Tableau' or the image canvas as defined by its boundaries.
4. A critical subset of of the tiles are the boundary pieces  - notably the 'edge' tiles (characterized by a single completely flat side) and the corners (with two sides and a 90° angle most of the time (unless you have a non-rectilinear shaped puzzle).

There are five or so methods to analyzing, and assembling/solving a 2-D puzzle:

1. What I call - 'brute force'; which is to look at the shape of the adjacent laid-out piece(s) and and find the matching piece that will fit. This is generally the method of last resort, typically when there are no other visual clues form the puzzle image, specially if you are working in an area of the image lacking any distinctive detail. You are generally left with 'plug' and/or 'socket' conditions, and curvilinear and/or flat edges that you will be trying to identify and match.
2. Contextual match of a color element, as well as possibly texture and tonality. This is a basic method of identifying a tile by way of matching a color or colors in context.
3. Contextual match of a graphic element. Another basic method of identifying a tile by way of matching a shape, or vector element.
4. Contextual match of a textual element. This one of the easiest methods to assembling a 'block' or 'portion' of a puzzle image, particularly large textual elements, usually a title element on the image. Smaller text - possibly captions - are somewhat tedious, but still a very useful way to identify tile and its relative location; or reduce the number of possible possibilities, at least.
5. Puzzle boundaries and corners. For me, this is the fundamental step to solving a jigsaw. It may very difficult - particularly for challenging jigsaws - to assemble the entire boundary initially, but it is usually one of the easier puzzle elements to complete over the span of the time of solution. 

Characteristics of a challenging jigsaw puzzle and basic approach to solving it

In the case of this 'Modern Locomotives' puzzle, we have a combination of elements: highly detailed images of locomotives (arranged in ascending order of date manufactured or operated - a useful clue, and most with distinctive coloration and texture), large titular graphic text,  graphic symbols (in this case national flags), captions (including basic facts about the locomotives; again, helpful clues in identifying tiles and their relative location), and of course, expanses of white background and a monotone blue border. What makes this puzzle particularly challenging is the high number of small pieces - each tile occupying an area of a square less than one inch, and many less than a 3/4" and even some less than 1/2". This leads to greater unpredictability, in determining the shape of tile to fill a given space. Sometimes what what may seem like a logical space for a single tile, has been deceptively arranged with two pieces - effectively delaying their identification (what I like to think of as 'capture'). 

The space reveals the criteria for what would seem logically to describe a single, roughly square, tile with two 'plugs' and two ''sockets'; however...

It was surprising to find that not the case here: that the space defined was in fact for TWO tiles, one of them being a tiny sliver of a tile...

... for the completed fit.

There is also a very high degree of tile variation: I would even say, no two tiles in this puzzle are alike. The solid border and white space are also complications. 

It is good to choose a very flat and firm surface on which to assemble the puzzle, such as a wood table. Recognize that a challenging puzzle may take a whole day or even days or weeks to solve (depending on how driven one is to solve it). The surface should obviously therefore be selected so that it can afford to be left as is or the duration. It is highly advisable to study the published size of the puzzle (even if it happens to be only an approximation). One might go as far as to mark or tape the corner points (if not the whole boundary) on the table surface. I actually only require know the size and I can mentally  visualize the puzzle size until sufficient pieces are placed. Understanding the actual boundaries of the  image, allows one to mentally map out the relative position of distinct portions or 'blocks' of the overall image. In the case of 'Modern Locomotive', there are the individual locomotives which form thirty-six distinct 'blocks', the main graphic title ('Modern Locomotives' and its three translations below it in French, Spanish, and German)

The main title graphic at the center top of the Jigsaw with translations in French, Spanish, and German underneath: relatively easy to identify pieces amongst all the tiles, pretty easy to assemble and place (because after all they spell definite words) and they provide a few important 'bridge' pieces to adjacent 'blocks'.

 as well as the flags of the nations represented on this tableau on either side of the title. The boundary could be said to be like a 'block' as well. 

This Jigsaw included national flags on either side of the main title graphic, which as colorful, graphic elements are relatively easy to find amongst a lot of tiles and relatively easy to arrange and place.

This fully formed void space reveals the criteria for the a tile having three 'sockets' and a single 'plug' on its bottom. Moreover, the tile's top slopes down to the right (kind of like Gumby's head!).  In this case, the tile includes the top of British loco which made it part of that 'block' and somewhat easier to solve.

This void defines a peculiar shape with opposing 'plugs' at one end a single, awkward 'socket' at the 'top' of the tile, and a third 'plug' to the right. Without either 'block', the tile is harder to identify than many by 'brute force', in spite of the unique shape. The little bit of caption helps a bit. The tiny bit of tack tie on the top is almost useless for identification.

As tile pieces are placed, adjacent tiles can be more easily identified. The more tile pieces that are placed, blocks of the puzzle get easier to solve as each tile place will reveal the criteria of the adjacent tile - i.e. edge shape, plug, and/or socket. Once enough tiles are laid, missing tile criteria will be more precise; number of plugs and/or sockets as well as arrangement of plugs and sockets (e.g.  a tile defined by two opposing plugs and two opposing sockets, or, say, a tile defined by an s-curve on one side the left side, widening at the tile at the bottom, a plug on the top, and sockets on the side and bottom). That said 'transition' zones between distinct blocks will tend to be hard to solve. These will be, again, areas of solid color (in this case white background), or relatively unvariegated areas of texture/tone and/or color. It is very useful to identify orientation of the tile by studying the image on it as well as studying the is side's shape, plugs, and sockets relative to the criteria revealed on the tableau of partially-formed blocks.

Note a repeating motif which can be as confounding as it is helpful: all rows of locos include a side view of track (steel rail on top of wood ties).  This at once helps to distinguish the orientation of a tile often without telling you on which row of locos it might be located.

Case Study: Methodology to Solving 'Modern Locomotives' Jigsaw

My usual first task is to separate out the boundary tiles into a simple pile. I will also be looking for the corner pieces to separate out. One could elect to place the corner pieces into their final positions  to establish the 'tableau'. I tend to wait until I can actual form a corner of several pieces (usually edge tiles), so as not to lose track of these pieces as the image forms. I then identify the most distinct image 'blocks' (selected because their composite tiles are easy to identify) and identify and separate out as many of these block pieces as can quickly be performed (usually 3 to 6 blocks of image). I will position these little piles in their relative position on the tableau. This tends to preclude having too many 'blocks' on the go initially at least. Most of these pieces will be identifiable simply by their distinctive color or colors. some, as in this case, by virtue of caption text that I happen to have read and could quickly decipher as being part of a given block. Soon In this puzzle, associated national flags will become identified as associated to a given block because of tile shape and adjacent caption. The piles of pieces  I collect will not usually form complete 'blocks'. This is not important.

The first block I actually laid is the graphic main title as this has clear graphic and logical clues to make it the easiest of all blocks to assemble. Some of the tiles describing the title will big over to one of the locomotive image blocks setting up relative location of that adjacent image block and shape of the adjacent tiles. I will first tend to assemble each of the other blocks for which I have created little piles of tile. These blocks will tend not to be complete, but complete enough to achieve significant and cogent portions of the image. Each of these blocks will also tend to inform the next adjacent block to form by virtue of several tile pieces that one might randomly identify of an adjacent block.

Boundary Tiles: note the solid border makes it difficult to lay initially as a 'block' ('boundary block'); but as adjacent (locomotive) 'blocks' are assembled, key 'bridge' pieces reveal where boundary tile are to be placed.

In this puzzle, as mentioned previously, the locomotives are arranged in ascending order of date of operation or production. This helps to identify caption text by virtue of finding a tile with a date on it. One can quickly compare the date to the key image on the cover of the box and place the text tile into its relative position on the tableau. another key clue in this puzzle are the national flags that appear under each locomotive. At least the number of positions that a repetitive flag occupy is critically reduced. Again, once placed, adjacent tiles can identified more easily.

A bright red Austrian 'Hercules' locomotive 'block'

In this puzzle, as the boundary is a solid color, the boundary 'block' took somewhat more time to form, though it was one of the first 'blocks' to be 'formed' (i.e. cogent, but not completely solved). Key pieces linking the solid border and other 'blocks' or captions permitted their placement into their relative positions. This revealed adjacent tile shape criteria (again, edge shape, plug, and/or socket). The first locomotive blocks formed tended to be the ones with the most distinctive colors. In this case yellow and red locomotives.

A bright yellow (and gray) DD40 Union Pacific Locomotive 'block'

A bright purple (and gray), with distinctive British Railways locomotive 'block' 

An Amtrak P42 with distinctive turquoise and gray livery 'block'. Also note national flags and descriptive captions under each loco.

 followed by purple and turquoise ones (roughly speaking). As the blocks formed several became solidly linked by virtue of transition 'bridges'. This in turn help to fix relative placement blocks and thereby reveal even more of the criteria of the adjacent missing pieces. As all the most colorful locomotive 'blocks' were formed, however, the box contained nothing but white background tiles, tiles with tiny bits of tonal colored image, or bits of captioned text. 'Brute force' methods became more prevalent in finding adjacent tiles; in other words, the edge shape criteria becomes the more obvious available information remaining in identifying the next tile. The tiny bit of image or color on a tile also needed to be studied more intently. These remaining pieces became the slowest and most tedious to 'solve', at least, until there where 30 or so single tiled holes remaining, which could filled very quickly to complete the whole jigsaw. 

I spent about eighteen or so hours over two days on this puzzle. 

Complete jigsaw puzzle

Please let me know if you have other good techniques!