Dichotomous key

Dichotomous keys are used to identify biological specimens by asking a series of questions.  At each step, two options are presented.  To use the key, tap on the option which best matches your specimen. The rows are coloured as follows:

      white background – this is the current choice (also called a couplet)

      yellow background – shows the choices already made

      grey background – choices that have been passed over, or have not yet been reached


One of the common mistakes when using such keys is not following the path correctly. To help prevent mistakes, this interactive key highlights the current choice, and only progresses to the next couplet if you tap on one of the current choices.  (If you tap on a grey background, nothing much happens; if you tap on one of the previous choices – a yellow background – you are offered the option to reset your progress to that point.)


The number on the left of the description is the couplet number.  The number on the right is the couplet that you will go to, if that choice is taken.


The Step Back button will undo a choice, that is, take you back one step in the key.  If you are already at the beginning of a key, it will take you back to the previous key if there is one.



In the illustration above, the user has selected “Without fins and gills” from the first couplet. This has led to couplet 4, at which point “Covered with scales, feathers, fur or hair” was selected. This has, in turn, led to couplet 5 which is where the user will make the next choice.


The sections below cover navigating multi-level keys, and the actions available from the popover menu.


Navigating multi-level keys

A couplet entry may end with a species name – tapping on this will take you to the detailed description and photos. For example:



Tap here to see more information on the Species Description.


Or a couplet may end with a link to another key.  Tap on that row to go to the new key.




The new key will slide into place, and the screen might look like this:




At the top left of the screen, the navigation buttons show which level of the key is being displayed.  There may be many levels to your keys depending on the particular subject matter.



You can still review the path you have taken to get to the new key by using the navigation buttons that will appear in the top left. Tapping on 1 will take you to the top level key, and so on.





Note that you can only Step Back from the current couplet.  So on the higher level keys (levels 1 and 2 here), there is no option to Step Back; instead, there is an option to return to the current couplet.



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The actions list provides a number of options you can take.



Reset Position


The Reset Position action allows you to go back to the beginning of the key.  In a multi-level key, you have the option either to go back to the beginning of the key you are on, or the entire key.  There is an option to save the current position before doing the reset.


Save Position / Show Saved Positions


At any time, you can use the Save Position feature to store your progress to that point.  This might be useful if you want to go back and explore a different route through the key but want to keep track of where you have got to. This action brings up the Save Position screen where you can add an (optional) name for this position.


To go back to one of the saved positions, choose the Show Saved Positions action. This will bring up a list of all your saved positions.  Tapping on a saved position will set your progress to that point.  Tap Edit, to delete a position or to change their order.


Show All / Show Paths Only


The next action affects how the key is displayed in the screen.  The default mode is Show Paths Only. In this mode, where a couplet is no longer reachable, because of the choices you have made, the couplet is hidden from view - this makes it easier to see your path through the key. However, it is sometimes helpful to see what you have passed over - tapping Show All will display the hidden couplets too. (They will have a grey background to show that they are not reachable given your current choices.) 


Show Paths Only

Show All

Browse Key


Finally, the Browse Key option puts the key into a different mode of operation, allowing you to leaf through it like a book.  In this mode, you can move through the whole key without making choices on couplets.  You do not use the key by tapping on couplets –  instead, you can tap on any row which has a 'Browse' label to navigate through the key.



To make it clear that you are not in interactive mode, the top bar is coloured differently. To return to the normal mode of operation, tap the Exit Browse Mode button.  This will reset you to the point you had reached in the normal key, before you started browsing.



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