​Preparing a passage plan is no more than a formal visualisation of the voyage you intend to take. And in familiar waters, simply running through the passage in your head is a great way to highlight specific issues or potential areas that require more consideration and/or preparation.

That said, making a more formal plan and actually writing it down helps you to establish what information needs to be collated and helps you to identify hazards and risks and summarise and distil relevant and important data. 

We all know from our school days, putting things down on paper helps us to crystallise our thoughts as well as highlighting our ‘workings’! Also, if things do go wrong, having evidence of a carefully prepared passage plan can be very useful - especially if the insurance company or the authorities become involved! 

Under SOLAS V Regulations, there is now a legal requirement for the skipper going to sea to compile a passage plan. We can all get into difficulties at sea, so planning to avoid as many pitfalls as possible is just common sense. 

For a map to be useful in helping to navigate and plan a voyage (us sailors call them charts) it must be properly understood and be accurate for its purpose.  Charts are physical (or electronic) representations of the physical characteristics of the earth & the water on it. They are a projection of a curved surface (the earth) onto a flat one (such as a sheet of paper or computer screen).

It's necessary to make some adjustments to how this information is presented so that this projection can be done whilst still making it a useful and navigationally accurate representation of the surface of this spherical planet.
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