and I apologize if this is the wrong SE for this question.
I am attempting to scale a map so that $1cm$ measured is $25,000cm$, real life ($1:25000$ scale). The maps original scale is unknown, and the projection is world-mercator.
My map distance width is $6800m$ real life, or $680000cm$.
$680000cm / 25000$ gives me $27.2cm$.
I then take that $27.2cm$ and multiply is by the printers dots-per-cm ($96 dpi / 2.54 cm/in = 37.79 dots-per-cm$) to get how many pixels wide the image will be for the printer, so $27.2cm * 37.79cm$, $1027.8$ (rounded up to $1028$ to avoid subpixels).
I print this out, and measure the entire map. It comes out to $27.2cm$, which multiplied by $25,000$ brings me back to $680000cm$. So far this seems good.
BUT, there is a small park in that map that measures $1.05km$ wide in real life, so $105000cm$. On the printed map, this measures out to be $18.8cm$, which is way too big ($18.8cm x 25000 is 470000cm$, which is way far off of $105000cm$.)
So measuring the whole map yields the correct result, but measuring small components in the map gives the incorrect answers. What do I need to do to ensure that the map is at a $1:25000$ scale so that each cm measured on the printed map is $25000cm$ in real life?