Polygons showing the extent and types of wetlands in Victoria based on photography taken during the 1970's and 80's.  Wetlands are classified into primary categories based on water regimes and subdivided into sub areas based on vegetation or hydologic attributes.
The polygon boundaries were derived from digitizing  marked up aerial photography interpretation.

Polygons showing the extent and types of wetlands in Victoria based on photography taken during the 1970's and 80's.  Wetlands are classified into primary categories based on water regimes and subdivided into sub areas based on vegetation or hydologic attributes.
The polygon boundaries were derived from digitizing  marked up aerial photography interpretation.

WETLAND_1994 is one of two layers designed to document changes over time in the nature and  extent of wetland environments in Victoria.  This layer is directly related to WETLAND_1788 via  the use of a common wetland identification system.  It is a more complex layer than  WETLAND_1788 in that there is delineation of sub areas within wetlands.

Precision: 10m to 100m
Determination: Deductive estimate.  Ad-hoc comparisons with 1:25,000 layer data  and various sorts of imagery indicated good correlation in terms of  shape and size but with errors of the order indicated above in terms of  position and/or rotation.  When resources permit, the 1:25,000 library  hydrology and roads layers should be used to identify layer  inconsistencies which may indicate specific wetlands which require  translation, rotation or boundary modifications.

The classification scheme used is based on photo interpretation and ground surveys carried out by Departmental research staff under the direction of research scientist Andrew Corrick.

The Wetland Mapping System includes processes for checking:  *node, label and intersect errors.  *validation of category codes prior to insertion in the library.

Dataset Source: The data has been prepared primarily from standard Survey and Mapping Victoria photo runs with  some local revisions based on other historical sources.

Dataset Originality: Primary

                            
                              Relationship to other Datasets: As stated above, this layer is closely related to WETLAND_1788 and should be maintained in a  way which ensures consistency between them in the use of identifiers and classification codes.   Comparisons of this layer with HYDRO100 and HYDROP100 should be made with caution as the definitions used in delineating and classifying wetlands are likely to be significantly different in some cases.

Current Design Issues: Although the only attributes held within this layer are an identifier and a wetland category/sub- category, there are several external tables in existence keyed on the same identifier.  These include  tables documenting RAMSAR wetlands, High Value wetlands, named wetlands and  wetlands  supporting breeding colonies of waterbirds.

The wetland category field consists of a primary category and a subcategory separated by a period.  The subcategories are not consistent between primary categories (eg: a redgum dominated sub area of a shallow marsh is coded 3.05 whilst the same subcategory in a meadow is coded 2.03 - not 2.05).  This has not been changed because if it was it would make reconciliation of layer codes with the source material very difficult.  Instead tables have been created which map real category codes to alternate codes which can be used consistently between primary categories (refer normcats.lut and gencats.lut).

Future Design Issues: It is envisaged that additional external tables will be defined which group wetlands in additional  ways according to specific attributes (eg: membership of large scale wetland systems).  Further  attributes may also be added to existing tables, but none of this work should require any change to  the structure of the library layer.

Related Documents: None