Title

Wetlands Extent for Victoria Prior to European Settlement - Deduced 

Alternate title

WETLAND_1788 

Purpose

WETLAND_1788 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_1994 via the use of a common wetland identification system. It is a simpler layer than WETLAND_1994 in that there is no delineation of sub areas within wetlands. 

Credit

Andrew Corrick 

Supplemental Information

Relationship to other Datasets: As stated above, this layer is closely related to WETLAND_1994 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, 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. 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 

Status

Completed  

Horizontal Accuracy

25m  

Code

4283 

Maintenance and update frequency

Not planned  

Topic category

• Inland waters

Use limitation

Data is available under licence. Access subject to custodial approval. 

Classification

Unclassified  

Statement

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 

Description

Collection Method: Aerial photograhy interpretation. 

Description

The data has been inserted into covers based on 1:100,000 mapsheet tiles via one or more of four processes: * Pre ARC/INFO data: Prior to the availability of ARC/INFO, an in-house developed digitizing program known as DIGIT running on a PDP11 computer at ARI was used. The marked aerial photography was positioned on a digitizer using two reference points corresponding to six figure grid references. These points defined the orientation and scale of the photograph. The arcs defining wetlands on the photograph were then digitized. The coordinates generated were then converted to be expressed as values relative to the grid reference used as the wetland ID and stored on disk for subsequent plotting. This existing digital linework and associated attribute data was subsequently imported into ARC/INFO via the use a FORTRAN based conversion utility which created GENERATE input files. Further errror checking and editing processes were then applied to bring data from this source up to a comparable standard to data entered directly into ARC/INFO. * Direct digitizing from aerial photography: A facility is provided in the Wetlands Mapping System to digitize data directly from aerial photographs. This facility uses the ARC/INFO photo registration process which requires a minimum of five tic points to be defined. This process is used for editing or adding individual wetlands. * Digitizing from 1:25,000 survey map overlays: Some 1:100,000 mapsheets have been processed by digitizing in ARC/INFO using marked up transparent overlays of 1:25,000 mapsheets. * Scanning of 1:25,000 survey map overlays: On more complex mapsheets the marked up overlays have been scanned into SCITEX format files. These files have then been converted into ARC/INFO GENERATE input files and imported into ARC/INFO for final editing and adding of attributes. 

Classification

Unclassified  

Attribute Quality

Comments

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. 

Positional Accuracy

Comments

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. 

Conceptual Consistency

Comments

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

Missing Data

Comments

All wetlands with an area of 1 hectare or more should be present. All wetlands with an area of 1 hectare or more should be present. 

Excess Data