In this new proposal a lot of clarifications has been made
in the section about contours and formlines compared to ISOM2000. But if the
aim is to truly standardize the way landforms are drawn on orienteering maps
all over the world the work has only started. The specification text still has
many uncertainities, contradictions and confusing statements. It seems that too
many different viewpoints have been mantained and adopted into the
specification without a proper discussion inside the commission. The end result
will probably be that regional, national and personal preferences on how to
draw contours will prevail. Below is an attempt to find the issues on contours
where the disagreements between different mappers seem the greatest.
Contour interval
The ability to easily
assess the steepness of the terrain is vital in orienteering. It is therefore
very important that the contour interval for orienteering maps is standardised.
The contour interval for orienteering maps is 5 metres. In flat terrain where
the slope is less than 5% (or the contours would be more than 7 mm apart) all
over the area, 2.5 metre contours may be used. It is not permissible to use
different contour intervals on the same map. The presence of a form line
between contours makes the terrain appear nearly twice as steep. (Does it? Formlines do look distinctly different from
contours, especially with the proposed new thinner look. Has there been tests
made on how experienced orienteers perceive the terrain on a map with or
without formlines?) It is therefore very important that form lines are
used sparingly. Form lines shall only be used to represent important landforms
that can not be shown using contours. Instead of using form lines, contours
should be shifted slightly up or down to better represent the important
landforms.
4.1 Landforms
The shape of the terrain is shown by means of contours,
aided by special symbols for small knolls, depressions, etc. This is
complemented in black by symbols for rock and cliffs. Orienteering terrain is
normally best represented with a 5 metre contour interval. While it is
important to show the smaller features of the terrain, such as re-entrants,
spurs, knolls and depressions, it is essential that an abundance of small
features do not hide the main features of the terrain, such as hills, valleys
and major fault lines. Excessive use of form lines must be avoided as this
complicates the map and gives a wrong impression of height differences. If the
representation of an area needs a large number of form lines, a 2.5 metre
contour interval provides a more legible alternative.
101 Contour
A line joining points of equal height. The standard vertical
interval between contours is 5 metres. 2.5 metre contour interval may be used
for flat terrains. Slope lines may be drawn on the lower side of a contour line
to clarify the direction of slope. They should only be placed in re-entrants
and depressions. A closed contour represents a knoll or a depression. Form
lines can be used to differentiate flat knolls and depressions from more
distinct ones. (How does this relate to the statement
”Only one form line should be used between neighbouring contours.” below? Can
formlines be used to represent flat knolls that are situated on top of
formlines? Or is the distinction between flat and distinct knolls only allowed
when there is no formline directly below? This is a common argument between
mappers and should be adressed in the specification, see further in the map
comparison below.) Relationships between adjacent contour lines are
important. Adjacent contour lines show form and structure. (Will there be some kind of ”guideline” or ”best practices”
released on how to show form and structure with contours? The specification
allows for a lot of ”artistic freedom”, but there is very little help on how to
actually draw contours.) Small details on contours should be avoided
because they tend to hide the main features of the terrain. Prominent features
such as depressions, re-entrants, spurs, earth banks and terraces may have to
be exaggerated. Absolute height accuracy is of little importance but the
relative height difference between neighbouring features should be represented
on the map as accurately as possible. It is permissible to alter the height of
a contour slightly if this improves the representation of a feature. This
deviation should not exceed 25% of the contour interval and attention must be
paid to neighbouring features. The smallest bend in a contour line is 0.25 mm
from centre to centre of the line (footprint 4 m). The mouth of a re-entrant or
a spur must be wider than 0.5 mm (footprint 8 m). The minimum length of the
longest axis of a contour knoll is 0.7 mm (footprint 10 m) from centre to
centre of the line. Smaller prominent knolls can be represented using the small
knoll or small elongated knoll symbol or they can be exaggerated on the map to
satisfy the minimum dimension. A contour depression must accommodate a slope
line, so the minimum length of the longest axis is 0.8 mm (footprint 12 m) from
centre to centre of the line. Smaller, prominent depressions can be represented
using the small depression symbol or they can be exaggerated to satisfy the
minimum dimension. Contour lines can be broken if they go through or touch
other brown symbols, except for broken ground. Contours must be adapted (not
broken) in order not to touch small and elongated knoll symbols. (If contours can be broken for small depressions but not for
small knolls there is a lack of symmetry in the way landforms are represented.)
Colour: brown.
102 Index contour
Every fifth contour shall be drawn with a thicker line. This
is an aid to the quick assessment of height difference and the overall shape of
the terrain surface. An index contour may be represented as an ordinary contour
line in an area with much detail. Small contour knolls and depressions are
normally not represented using index contours. An index contour may have a
height value assigned. A height value should only be inserted in an index
contour in places where other detail is not obscured. It shall be orientated so
that the top of the label is on the higher side of the contour. The index value
(label) shall be 1.5 mm high and represented in a sans-serif font (not bold,
not italic). Colour: brown. (In areas with small height
differences index contours are mostly disturbing the map picture. In Finland it
has been common practice to not use index contours when the total height
differences between lowest and highest point on the map is less than ten
contours. This practice makes a lot of sense.)
103 Form line
Form lines are used where more information must be given
about the shape of the ground. They shall not be used as intermediate contours.
(Does this mean that formlines should not be assigned
to an intermediate 2,5 meter level on a map with 5 meters contour interval? And
are they also exempt from the 25% alteration rule for contours? This is a
common argument between mappers and should be addressed more clearly in the
specification.) Form lines are
used only where representation cannot be made complete with ordinary contours.
Only one form line should be used between neighbouring contours. It is very
important that a form line fits logically into the contour system so the start
and end of a form line should be parallel to the neighbouring contours. (Here the word ”neighbouring” is used twice without any
clarification to what it means. How close do the contours have to be to be
”neighbours”? Or does ”neighbouring” mean the nearest contours regardless how
far away they are? Is it even allowed to use open formlines in flat terrain
where there are no neighbouring contours?) The gaps between the form
line dashes must be placed on reasonably straight sections of the form line.
Excessive use of form lines must be avoided as this disturbs the three
dimensional picture of the ground shape and will complicate map reading. (This sounds like a total contradiction to the statement
”Absolute height accuracy is of little importance but the relative height
difference between neighbouring features should be represented on the map as
accurately as possible.” above. Using
formlines is in many cases the only way to represent relative height difference
between neighbouring features. But where do we draw the line between excessive
and not? Clarification needed!)Minimum length (non-closed): two dashes
(2.7 mm - footprint 41 m). Minimum length of the longest axis of a form line
knoll or depression: 1.0 mm (footprint 15 m) from centre to centre of the line.
Colour: brown. (Are slopelines allowed on formlines?
They should be, and not only in reentrants like on contours.)
Map comparison
The maps should be easy to find even if these links die.
Map 1: Typical
finnish map (Jukola 2015)
Map 2: Typical Swedish
map (Swedish Middle Championships 2015)
Both of these maps are considered good, but despite similar
terrain the mapping styles used for contours are completely different.
Map 1 never uses formlines and contours to distinguish
between knolls of different height. Instead formline knolls are always used on
top of contours and contour knolls are always used on top of formlines.
Formline knolls are never drawn on top of open formlines. Formlines are
generally long and are often used as intermediate contours. This gives a very clear
three dimensional picture of the ground shape, but it doesn’t show relative
height differences between neighbouring features as accurately as possible. The
map does not have index contours at all.
Map 2 uses formlines and contours to distinguish between
knolls of different height all the time. Formline knolls are sometimes drawn on
top of open formlines. Formlines are sometimes quite short and are never used
as intermediate contours. This shows height differences between neighbouring
features accurately but the three dimensional picture of the ground shape is
more unclear. The map has index contours but they add almost nothing to the map
and are mostly disturbing.
So does map 1 or map 2 implement the intentions of the
authors of ISOM201X when it comes to contours? Or do they both? Or none?
