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.
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.
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.
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.)
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?
Skicka en kommentar