Appendix I1: Examples of NVIS spatial linkages[1]
The way in which the contents of the spatial data and closely-related tables have been structured in practice is best illustrated by looking at some extracts of records from the relevant tables. The inter-convertibility of the spatial information and what is meant by “flat” and “deep” table structures should become clearer by examining these tables[2]. The same or related records are illustrated in all extracts below, with the colouring[3] used to track records across the two spatial formats (SPATIAL_DATA and MAP_UNIT). In the following example, from the Flinders Ranges in South Australia, the vegetation type labelled as FR002 (NVIS_ID=50151) is the most extensive in six mapping units. In one unit it is the only vegetation type present; in the other five it is accompanied by other described types (FR004, FR005 and FR008) in various permutations. In NVIS version 4.2, the vegetation type FR0002/50151 is also present in seven other mosaics[4] in a minor position – i.e. other than the first.
VEG_DESCRIPTION table example
The structure of the VEG_DESCRIPTION table (Table 20) is relatively straight-forward. Many of the fields in this table are quite long and hence difficult to display. Hence in this example, the more complex levels of the NVIS hierarchy have been left blank. The records of vegetation descriptions in this table (referenced by NVIS_ID) are those referred to in the spatial data examples below.
Table 20 Extract from VEG_DESCRIPTION table, with only some fields shown
NVIS_ID / SOURCE CODE / LEVEL OF DETAIL / NO. OF STRATA / L1_CLASS / L2_STRUCTURAL_FORMATION / L3 / L4 / L5 / L6 / SOURCE_DESCRIPTION / ENVIRONMENTAL_DESCRIPTION /50151 / FR0002 / level6_sub_association / 2 / Samphire shrub / Low open samphire shrubland / shrub / Swamps and Closed drainage depressions;Drainage lines, floodouts, lakes and Run-on landforms;Saline;Swamps and low-lying depressions
50153 / FR0004 / level6_sub_association / 3 / Shrub / Tall open shrubland / shrub / Terraces and Floodouts;Drainage lines, floodouts, lakes and Run-on landforms, surrounding ranges;Clay to Sand/Loam;Alluvial;Assoc with water courses and low-lying areas
50154 / FR0005 / level6_sub_association / 1 / Shrub / Shrubland / shrub / Floodouts;Drainage lines, floodouts, lakes and Run-on landforms, surrounding ranges;Clay to Loam;Alluvial, saline;Terminal floodouts
50157 / FR0008 / level6_sub_association / 2 / Chenopod shrub / Low chenopod shrubland / shrub / Plains;Plains and rises;Clay to Clay/Loam/Sand;Hard soil
1.
Spatial_Data example
This is the attribute table attached to the spatial data (Table 21). It demonstrates a “flat” or horizontal table structure with one record[5] per MAPUNT_IDENTIFIER. This structure is the most practical for using in a GIS. Successive vegetation associations within a mosaic are identified by attributes NVISDSC1, NVISDSC2, NVISDSC3[6] etc. across the table. In this example, mosaics have been identified and resolved into the component vegetation types. However, the type of mosaic has not been specified and the (unmapped) proportions within each mosaic have not been recorded.
Table 21 Extract from SPATIAL_DATA (The colours are used to track record linkages and are specific to this Appendix).
MAPUNT IDENTIFIER / NO OF VEG DESC / SPATIAL MIX / NVISDSC1 / NVISDSC2 / NVISDSC3 / NVISDSC4-6(not shown) / VEG PROP1 / VEG PROP2 / VEG PROP3 / VEGPROP4-6
(not shown)
59102832 / 1 / pure / 50151 / 0 / 0 / 0 / 0 / 0
59101270 / 2 / mosaic unknown / 50151 / 50153 / 0 / 0 / 0 / 0
59101271 / 3 / mosaic unknown / 50151 / 50153 / 50154 / 0 / 0 / 0
59101272 / 2 / mosaic unknown / 50151 / 50154 / 0 / 0 / 0 / 0
59101273 / 2 / mosaic unknown / 50151 / 50157 / 0 / 0 / 0 / 0
59101274 / 3 / mosaic unknown / 50151 / 50157 / 50153 / 0 / 0 / 0
MAP_UNIT Table example
The MAP_UNIT table (Table 22) demonstrates a “deep” or vertical structure for the spatial data which is a more efficient structure in a relational database. It contains several records per MAPUNT_IDENTIFIER, one for each vegetation association within a mosaic, successively down the table. The codes within the NVIS_ID field refers to the NVIS_IDS in the VEG_DESCRIPTION table above.
Table 22 Extract from MAP UNIT table (The colours are used to track record linkages and are specific to this Appendix).
MAPUNT IDENTIFIER / NVIS_ID / SPATIAL MIX / NUMBER OF VEG DESC / VEG DESC POSITION / VEG DESC PROP'N /59102832 / 50151 / pure / 1 / 1 / 100
59101270 / 50151 / mosaic unknown / 2 / 1 / -9999
59101270 / 50153 / mosaic unknown / 2 / 2 / -9999
59101271 / 50151 / mosaic unknown / 3 / 1 / -9999
59101271 / 50153 / mosaic unknown / 3 / 2 / -9999
59101271 / 50154 / mosaic unknown / 3 / 3 / -9999
59101272 / 50151 / mosaic unknown / 2 / 1 / -9999
59101272 / 50154 / mosaic unknown / 2 / 2 / -9999
59101273 / 50151 / mosaic unknown / 2 / 1 / -9999
59101273 / 50157 / mosaic unknown / 2 / 2 / -9999
59101274 / 50151 / mosaic unknown / 3 / 1 / -9999
59101274 / 50157 / mosaic unknown / 3 / 2 / -9999
59101274 / 50153 / mosaic unknown / 3 / 3 / -9999
Discussion
The data in the two tables immediately above is directly equivalent. The fields MAPUNT_IDENTIFIER, SPATIAL_MIX, and NUMBER_OF_VEG_DESCRIPTIONS are common to both, (other than limits to field names in the SPATIAL_DATA). NVIS_ID in the MAP_UNIT table is equivalent to NVISDSC1, NVISDSC2, NVISDSC3 etc. VEG_DESC_PROPORTION (MAP_UNIT table) is equivalent to VEG_PROP1, VEG_PROP2, VEG_PROP3 etc. VEG_DESC_POSITION in the MAP_UNIT table is identified by the numeral in the attribute name of the attributes NVISDSC1, NVISDSC2, NVISDSC3 in the SPATIAL_ DATA. Note that the examples in the records above utilize up to three vegetation descriptions within a spatial unit; up to six are permissible as per the detailed NVIS structure diagram.
The SPATIAL_DATA structure is best suited to the spatial (GIS) systems environment and likewise the MAP_UNIT table to a database environment. However, both configurations of the spatial data have a vital role to play in the NVIS system. For example, to query the spatial coverage for a particular vegetation association the NVIS_ID in the VEG_DESCRIPTION table must be joined to each NVISDSC in the SPATIAL_COVERAGE in turn. It would be more efficient to conduct a single query within the database, linking the NVIS_IDs in the MAP_UNIT and VEG_DESCRIPTION tables to identify all spatial units where the association is found, whatever its position in a mosaic. In practice, the querying of mosaic contents is best done algorithmically using a procedural computer language, such as Perl or Python; see Figure 6—also included for reference below.
Figure 6 (repeated) Overview of the NVIS Vegetation Attribute Structure V7.0.
The NVIS database comprises data arranged in four different subsystems. Three of these subsystems are shown here. These are vegetation spatial data; vegetation description plus map unit attributes and detailed vegetation attributes. For simplicity, the tables and attributes for dataset information are not shown. The arrows, here, represent data flows, rather than formal relationships between objects. See Appendix C for a more complete diagram.
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[1] Adapted from unpublished NVIS material prepared by G. Rozenbilds.
[2] In the table, the attribute names and values have been truncated and/or omitted to fit the material into a manageable space.
[3] These colours are not related to the NVIS components elsewhere in this Manual.
[4] These are not shown in these examples.
[5] Assuming multipart polygons (ESRI, 2017). In practice, NVIS spatial data is usually managed in single-part polygons.
[6] This extends to a maximum of six veg types in a mosaic.