
== Customising the map ==

You can completely change which features are displayed and at what zoom
levels.

First you need to understand a little about the way that the zoom works
in Garmin maps.  There are two concepts 'resolution' and 'level'.

# The first is 'resolution' this is a number between 1 and 24 with 24 being
the most detailed resolution and each number less is half as detailed.
So for example if a road was 12 units long at resolution 24 it would be
only 6 at resolution 23 and just 3 at resolution 22.

On a Legend Cx the resolution corresponds the these scales on the device:

16  30km-12km
18  8km-3km
20  2km-800m
22  500m-200m
23  300m-80m
24  120m-50m

It may be slightly different on different devices.  There is an option
to increase or decrease the detail and if you change that from 'Normal'
then it will change the values above too.

# The next is 'level'.  This is a number between 0 and 16 (although perhaps
numbers above 10 are not usable), with 0 corresponding to the most
detailed view.  The map consists of a number of levels starting (usually)
with 0.  For example 0, 1, 2, 3 and a different amount of detail is added
at each level.

The map also contains a table to link the level to the resolution.  So
you can say that level 0 corresponds to resolution 24.

You can specify this mapping on the command line, for example:

  --levels=0:24,1:22,2:20

This means that the map will have three levels.   Level 0 in the map will
correspond to resolution 24 (the most detailed), level 1 will show at
resolution 22 (between scales of 500m and 200m) and so on.

== The map features file ==

Take a look at the map-features.csv file in the resources directory of the
mkgmap distribution.  It may be easier to edit it in a spreadsheet
program.

A typical line may look like this:

 point|amenity|grave_yard|0x64|0x03|23

* Column 1 is point, polyline or polygon, depending on whether the
  feature is a point of interest, a line feature such as a road or an
  area such as a park.

* Columns 2 and 3 are taken exactly from the '''key''' and '''value'''
  columns from the [[map features]] page.

* Column 4 is the garmin code that you want to use.

* Column 5 only applies to points and also determines the type of the
  object.  The file garmin_features_list.csv (also in the resources
  directory) has a list of all the values that I know.

* Column 6 is the minimum resolution at which this feature will appear 
  So in the example here where the resolution is 23 and we had
    --levels='0:24,1:22'
  it would show only at level 0.  If instead we had:
    --levels='0:24,1:23'
  it would show at both level 0 and level 1.
