The purpose of the conservation ranking system is to provide an accepted, composite means by which the conservation values of different areas, representing different features, can be ascribed, mapped and compared. The initial aim is to incorporate ecological, heritage, recreational and landscape components into a single ranking system. Other objectives for the ranking system require that the system be:

• simple to define for a given habitat or site;

• repeatable with minimal subjectivity;

• fully documented so as to be understood by key stakeholders; and

• well suited for mapping using a Geographic Information System.

As stated above and in the Study Brief, it is desirable that the conservation ranking system incorporate ecological, heritage, recreation and landscape components. However, the data collection effort devoted to this survey has generated an extensive database of ecological information and thus considerably more data are available to support the ecological component than the others. For this reason, and because of the expected variety of values attached to different components by stakeholders, it would not be appropriate for the system to "trade-off" ecological value against any of the remaining three components by weighting all components equally.

It was, therefore, proposed (in TR1) to construct the ranking system to consist of scores A, B, C and D corresponding to the high, medium, low and negligible ecological values outlined in the previous section. These scores would be assigned to areas whose boundaries are defined by their habitat type and ecological value. If that area is also found to contain areas or sites of heritage, recreational or landscape value, the area would be awarded a single "+" for each component. The range of possible scores and their definitions are given in Table 3.2a.

As noted above, the heritage, recreational and landscape values are ranked as either present or absent for each area classified by ecological value. The criteria proposed for assessing whether these values are present or absent were presented in TR1 and revised based on further liaisons with Government Departments and reviews of existing information.

In addition to the classifications of high, medium, low and negligible ecological value, the habitat base map has also included an asterisk ("*") to indicate that the area has one or more unique features which distinguish it from other areas in the same category. Feature(s) of a site which could be considered as "unique" and might deserve designation of an asterisk "*" include(s):

• being one of the few or the only remaining breeding/nesting habitat(s) for "rare" species; or

• being one of the few or the only pristine (free from human disturbance) site(s) of a particular habitat type remaining in Hong Kong; or

• being unique in its structure and/or function which has distinguished the area to be somewhat better than other areas of the same habitat type.

The "high*" designation would thus signify that the area has extremely high ecological value and is a priority area for protection. The asterisk could also be used for medium, low or negligible categories to indicate that the characteristics of the area are somehow better than other areas in the same category.