Time series
The term “time series” refers to a chronologically arranged sequence of geodata sets.
At swisstopo, time series are regarded as an additional aspect of current products. They result out of the fact that the Federal Office of Topography has now been producing geodata for the same regions for more than 170 years at varying intervals. Time series are therefore a result of historical preservation, i.e. the process of securing and permanently storing all earlier versions of maps and geodata sets. To date, swisstopo has kept all of it’s geodata. Therefore it is possible for swisstopo to make time series available.
All map sets produced by swisstopo have been documented in the map collection. On average, each sheet in the National Map series is updated every six years in accordance with the updating cycle introduced in the 1960s, A clearly defined cycle has not yet been defined for older series of maps, instead their updating has been carried out on an ad hoc and temporary basis depending on the momentary needs. In terms of periodicity, the criteria for aerial images are similar to those for the National Map series for which the photos were taken, though strictly speaking the term “updating” cannot be applied to aerial images.
A prerequisite for the formation of time series is that the geodata sets involved all share the same characteristics (e.g. the scale, perimeter and data type must all be the same in a given data set). For example, it makes little sense to change from a “map” data type to a “orthophoto” within a particular data set.
The production and content of the various National Map series have always been based on the applicable rules with regard to recording the current status of the landscape. The creation of time series to document landscape changes was not the main objective, but may rather be regarded as a logical consequence of the lengthy timeframe encompassed by swisstopo’s production activity. Taking that into account, certain restrictions arise with respect to the use of swisstopo geodata time series which primarily concern the National Map collections. In questionable cases it is therefore advisable to also refer to other sources such as aerial images, field notes and evaluation slides, and to consult other photos or experts in order to avoid false conclusions.
Incomplete updating
Certain landscape elements such as glaciers and forests should be treated with caution when dating is carried out on the basis of the update status of the National Map. At times it was not always possible to fully update such elements at with the necessary degree of completeness due to capacity reasons.
Changed guidelines
Furthermore, it should be noted that, due to changed cartographic illustration guidelines, some elements no longer appear on maps from a certain time onwards, even though the landscape itself has not actually changed. An example of the changed guidelines is illustrated below (railway embankment between Sissach and Böckten): with effect from the 2000 edition, the railway embankment between Sissach and Böckten (which is between 5 and 6 metres high) is no longer shown due to the changed cartographic illustration guidelines.
All map sets produced by swisstopo have been documented in the map collection. On average, each sheet in the National Map series is updated every six years in accordance with the updating cycle introduced in the 1960s, A clearly defined cycle has not yet been defined for older series of maps, instead their updating has been carried out on an ad hoc and temporary basis depending on the momentary needs. In terms of periodicity, the criteria for aerial images are similar to those for the National Map series for which the photos were taken, though strictly speaking the term “updating” cannot be applied to aerial images.
A prerequisite for the formation of time series is that the geodata sets involved all share the same characteristics (e.g. the scale, perimeter and data type must all be the same in a given data set). For example, it makes little sense to change from a “map” data type to a “orthophoto” within a particular data set.
The production and content of the various National Map series have always been based on the applicable rules with regard to recording the current status of the landscape. The creation of time series to document landscape changes was not the main objective, but may rather be regarded as a logical consequence of the lengthy timeframe encompassed by swisstopo’s production activity. Taking that into account, certain restrictions arise with respect to the use of swisstopo geodata time series which primarily concern the National Map collections. In questionable cases it is therefore advisable to also refer to other sources such as aerial images, field notes and evaluation slides, and to consult other photos or experts in order to avoid false conclusions.
Incomplete updating
Certain landscape elements such as glaciers and forests should be treated with caution when dating is carried out on the basis of the update status of the National Map. At times it was not always possible to fully update such elements at with the necessary degree of completeness due to capacity reasons.
Changed guidelines
Furthermore, it should be noted that, due to changed cartographic illustration guidelines, some elements no longer appear on maps from a certain time onwards, even though the landscape itself has not actually changed. An example of the changed guidelines is illustrated below (railway embankment between Sissach and Böckten): with effect from the 2000 edition, the railway embankment between Sissach and Böckten (which is between 5 and 6 metres high) is no longer shown due to the changed cartographic illustration guidelines.
LK25, sheet 1086, first edition, 1955
LK25, sheet 1086, current version, 2006
Problem of subjectivity in the map production process
It is never possible for human beings to be fully objective, no matter how hard they try. In their daily activities, topographers in the field as well as office staff constantly have to make decisions which at a later date they probably would not have made, or which turn out not to be the best answer to a (future) specific issue. Below is an example of this problem which at first glance appears unspectacular, but is nonetheless symptomatic: the Brunnmatt creek near Sissach was no longer illustrated between the first edition of LK25 and the complete update in 1994, even though it was never filled in or covered over.
It is never possible for human beings to be fully objective, no matter how hard they try. In their daily activities, topographers in the field as well as office staff constantly have to make decisions which at a later date they probably would not have made, or which turn out not to be the best answer to a (future) specific issue. Below is an example of this problem which at first glance appears unspectacular, but is nonetheless symptomatic: the Brunnmatt creek near Sissach was no longer illustrated between the first edition of LK25 and the complete update in 1994, even though it was never filled in or covered over.
Final edition of First edition of Complete update of Complete update of
TA25, sheet 30 LK25, sheet 1068 LK25, sheet 1068, LK25, sheet 1068,
(Liestal), 1940 (Sissach), 1955 1988 1994
No means of direct comparisons due to differing geometries
Aerial images are central projections and thus produce a distorted picture of the landscape. This means that, strictly speaking, they cannot form time series because of the differing geometries. For many users, however, this is no problem because it is sufficient for them to make pictorial comparisons in which geometrical aspects can be overlooked. But as soon as direct superposition is required (e.g. in a geographic information system), geometry becomes a decisive factor.
Data sets without time series
There are also geodata sets from swisstopo that do not contain time series: for example, terrestrial images that were used between 1915 and 1947 for producing the 1:50,000 National Map and the 1:100,000 fortification maps, and which were subsequently replaced by aerial images when these maps were updated. Other data sets that do not contain time series include lake depth soundings and in particular geological maps, as well as certain thematic maps.
Aerial images are central projections and thus produce a distorted picture of the landscape. This means that, strictly speaking, they cannot form time series because of the differing geometries. For many users, however, this is no problem because it is sufficient for them to make pictorial comparisons in which geometrical aspects can be overlooked. But as soon as direct superposition is required (e.g. in a geographic information system), geometry becomes a decisive factor.
Data sets without time series
There are also geodata sets from swisstopo that do not contain time series: for example, terrestrial images that were used between 1915 and 1947 for producing the 1:50,000 National Map and the 1:100,000 fortification maps, and which were subsequently replaced by aerial images when these maps were updated. Other data sets that do not contain time series include lake depth soundings and in particular geological maps, as well as certain thematic maps.
Contact
Swiss Federal Office of Topography
Map collection
Seftigenstr. 264
CH-3084 Wabern
Tel. +41 31 963 21 11
Fax +41 31 963 24 59
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