How to handle TIME in GIS?

Question

Is there any way or any idea on how to handle Time attribute in GIS? For example, which are the ways to specify that an object is at a place at a given time interval and them it is in another place in another time interval, let's say, like a political boundary that has changed.

Answer 1

As always, it depends ... :-)

I see at least 3 different scenarios when time is involved.

1) The time part is different inside a geometry. A track log from a GPS for instance, if you make a linestring from that. Then you will have different timestamps for each vertex inside the linestring, and you can interpolate a calculated time at any place on the edges.
2) You have two different geometries, in your example political boundary that has changed over time.
3) You want to handle for instance different average temperature at a location over time.

If we start with number 3, it is only about the attribute data. Then you should store the geometry with a unique id and reference that id in a attribute table.

Number 1 in my list requires some sort of internal storage handling time as a dimension or at least extra information to each vertex. Often there is a possibility to store something as m, like x,y,z,m. I guess there is also systems handling date format like that. Otherwise you will have to handle time in some decimal format.

Number 2 in the list: Let's say that it is about countries and we are working with polygon representation. Then I would start with a table with attribute data about the countries. Every country has it's own unique id. Then I would put all the polygons no matter when in time they were valid in a table with a start and end field with information when they were used. In this table every polygon is unique and also keeps a foreign key referencing the country table. That relation is many to one. Many polygons represent one country.

So if we compare number 2 and 3 in the list, the point is that in 2 there is many gemetry representaions for one attribute representation (it is the geometry that changes over time). In number 3 it is the attributes that changes over time.

Some thoughts

Regards
Nicklas

Answer 2

QGIS can handle spatio-temporal data with Time Manager plugin. Features can have either one timestamp or two specifying start and end time.

Answer 3

In the case of changing political and other administrative boundaries I think the Great Britain Historical GIS had a good way of handling the problem, the structure of the data base is described at http://onlinelibrary.wiley.com/doi/10.1002/9780470987643.ch13/pdf and a large number of related papers can be seen at http://scholar.google.com/scholar?hl=en&q=GBHGIS+data+structure.

Basically every polygon was stored with a start and end date attached (though in some cases the date was a string like "sometime in reign of Charles I" I think we fudged those with dates of the kings reign) then it was possible to use a simple SQL Query (or OGC Filter for the web maps) to extract all the relevant polygons for any date.

Answer 4

ArcGIS 10 has it covered well

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Supported_field_formats/005z00000006000000/

and best practices http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Best_practices_for_storing_temporal_data/005z00000005000000/