2.5.5 Theme
The theme is the geological description of the data contained in the layer. As with the service title theme, the layer title theme should be a descriptive phrase in the service language. For English services the layers will most commonly have titles such as "Bedrock Age", "Bedrock Lithology" etc.
As mentioned above the layer names are for the consumption of the WMS software. It is important that within the OneGeology portal the layer names are unique. The data owner is responsible to guarantee that there is no layer name duplication in all the layers they provide (the same kind of requirement we have for urn administration in GeoSciML).
When we first started defining the rules for the OneGeology portal we discovered that MapServer has a 20 character maximum limit on LAYER names, to get over this issue, we defined a set of two and three letter codes to describe the most common layer themes to be used in the layer names, these are described below:
BA — Bedrock Age
BLT — Bedrock Lithology
BLS — Bedrock Lithostratigraphy
SLT — Superficial Lithology
SLS — Superficial Lithostratigraphy
MSF — Major Structural Features
This list is not exclusive, so please create your own if need be, or, if you think that other participants might want to serve the same type of data, you could post a message on the OneGeology forum for discussion of an agreed code.
Note, if you decide to use ESRI ArcGIS server (versions 9.3.1 and below) you will not be able to conform to this layer naming convention, because the software auto-names the map layers 0, 1, 2... We have discussed this issue at a senior level in ESRI-USA to see if this can be worked around, but it cannot for the time being. This problem will be dealt with in the OneGeology Registry through the use of auto-generated unique id’s for each registered service layer, this is necessary as in a Catalogue like that for OneGeology one cannot have two layers having the same name i.e. both being named layer name 0.
Section last modified : 19 January 2010.
