> For a given layout the locations next to blocks are unusable. In the layout above there are 3 **wasted spaces**. In another layout
> there is one **wasted space** less.

**wasted** (adj.)

> Unprofitably used, made, or expended
> **wasted effort**  
>[M-W][1]

> Not exploited or taken advantage of   
> *a wasted opportunity*  
>
> Useless or unprofitable  
> *wasted effort*  
>[Collins][2]

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> Crucially, you will start to see little islands of space where there
> are no pen lines whatsoever. These areas are usually cut off by an
> intersecting route and therefore rendered essentially **unusable.**
> Such dead, **wasted spaces** are critical in adding usable floor area,
> especially in flats or apartment blocks where physically adding square
> footage by extending in not an options.  
>[Laura Clark; *The Handbook of
> Home Design*][3] (2023)

> Where there is utility, it is invented and springs forth after the
> fact, as in the case of the spandrels of the Basilica di San Marco,
> which ended up being used, much later, as mere decorations. Originally
> drab and **useless**, these **wasted spaces** now have the accidental
> function of letting the golden light of Byzantine mosaics shine
> brighter.  
>[Barbara Stiegler; "1880: First Philosophical Critique of
> Adaptationism" in Martin Hartmann and ‎Arvi Särkelä (eds.);
> *Naturalism and Social Philosophy*][4]  (2023)

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*Unavailable* can imply that something is currently occupied, is being used for another purpose, or has been designated for some future use. *Wasted* usually means serving no purpose (*unused/unusable*) or a purpose of little value, connoting a missed opportunity. 


  [1]: https://www.merriam-webster.com/dictionary/wasted
  [2]: https://www.collinsdictionary.com/dictionary/english/wasted
  [3]: https://www.google.com/books/edition/The_Handbook_of_Home_Design/rxhjEAAAQBAJ?hl=en&gbpv=1&dq=unusable%20%22wasted%20spaces%22&pg=PT332&printsec=frontcover
  [4]: https://www.google.com/books/edition/Naturalism_and_Social_Philosophy/X1mjEAAAQBAJ?hl=en&gbpv=1&dq=unusable%20%22wasted%20spaces%22&pg=PA66&printsec=frontcover