Let’s take a look at addition and division mapping of natural and landuse. First we will look at the inconveniences that exist when mapping such areas. Next we will look at the method behind division mapping and scenarios of how to apply it. And finally take a real world example of how these two mapping styles were applied.
The definition of addition mapping is the act of adding new data to a white spot area aka an area with no data.
The definition of division mapping is the act of taking an existing object and dividing it down into smaller partitions.
Inconveniences when mapping natural and landuse
There are two main inconveniences when mapping natural and landuse from aerial imagery. First, depending on the resolution of the imagery, deciding where to make a clear cut if it is a distinct natural or landuse area. And second, the amount of clicking required to create a new area.
For the first inconvenience, more or less, it is personal choice and level of details. E.g. try to answer this question: when would one make a distinction between
natural = scrub and
natural = wood? The difficulty exists in the fact that the value
scrub permits trees and lots of time these trees are/aren’t growing close enough to each other.
For the second inconvenience, lots of editors have the option to split a way (aka division mapping). In JOSM you can split an area with
ALT+X (UtilsPlugin2 required). Or manually split the circumference of an area at two nodes and then separately connect the two arcs.
UtilsPlugin2 - Split Object tool
Let’s say one needed to create 4 square farmlands in a grid layout. How many node clicks are required?
Mapping the traditional way (aka addition mapping) 16 node clicks are required. One square has 4 nodes, and there are 4 squares, so
4 * 4 = 16.
Mapping with UtilsPlugin2, it takes 8-10 node clicks. There are two methods to achieve this. The first step is equivalent for both methods by drawing the circumference which is 4 node clicks.
- Draw the half line of the circumference which is 2 node clicks and split it in half with
ALT+X. Now one will have two rectangles.
- Repeat the process on both of the rectangles,
2 * 2 = 4.
- The total node clicks is
4 + 2 + 4 = 10.
- Draw the one half line of the circumference which is 2 node clicks.
- Draw the second half line of the circumference which is 2 node clicks, so that the two half lines make a cross.
- Select the two half lines and
SHIFT+Ito add nodes at the intersection. This in return will already select the one node.
- Select one of the half lines and
Pto split the way.
- Now select the larger of the half lines and
ALT+Xand do the same with the smaller ones.
- The total node clicks is
4 + 2 + 2 = 8, (though more interaction with the keyboard and lines is needed).
In this simple example there is already an improvement in node clicks. Next we will look at splitting larger areas.
Splitting a large area
Let’s say there is a 200 node circumference as
circum# and one needs to split it in half. Let
split# be the count of nodes for a split line with the minimum being 2.
With the UtilsPugin2 one just needs to add the split line with a minimum of 2 node clicks, select it, and execute
Total node clicks are
split# (minimum 2).
One does not have access to UtilsPlugin2, which is the case when not using JOSM. Thus choose the two nodes where to create the split of the circumference at. Then draw the split line and connect it to one of the circumference halves and do the same thing for the other half.
Total node clicks are
2 + 2 * split# (minimum 6).
Scenario 3 (not recommended)
One is not familiar with the split methodology and thus one starts the area anew (not recommended since the history of the nodes is lost). Draw the first area which has
split# + circum# / 2 node clicks and do the same for the second area.
Total node clicks =
2 * (split# + circum# / 2) = 2 * split# + circum# (minimum 204).
Planning on how to map natural and landuse
Let’s say one is mapping in an area that already has existing natural and landuse areas. One should plan ahead of how to map the white spots, since one can predispose oneself to inefficient mapping.
Let’s take a look at this animation of natural and landuse contribution in Croatia.
A shows white spot mapping, where as area
B shows the split method.
Choosing the correct tool for the circumstance
From above we learnt that JOSM can handle both area
B, though the downside of JOSM is that it is PC bound. On the other side Vespucci can handle also both, but being less efficient for
B compared to JOSM.
Thus to min-max one’s daily living, if one commutes or has other spouts of down time, one could use the time to map via Vespucci, especially the
A areas, since these areas are fairly straightforward and mundane to map. And once one has access to a PC, one can take upon the task of splitting up the newly mapped areas like in
In conclusion there are two ways of contributing natural and landuse data, either by addition (seen by white spot mapping) or through division (seen by the splitting method).