Saltmarsh habitat was hand digitalised from aerial images using ArcMap 10.3.1.

The layer was developed to assist with the identification of ecologically significant areas in the coastal area of Northland as part of the development of the new Regional Plan.

The primary purpose of this project was to identify all saltmarsh habitats, using the most recent aerial images available. A number of aerial image data sets have been used spanning over 10 years. Different aerials images have even been used in the same estuary or harbour. There are therefore limitations to using the layer for other purposes. For example, for any specific estuary or harbour unless the same aerial image, with the same date was used, the layer should not be used as a ‘habitat map’or for comparisons over time.

Saltmarsh habitat was hand digitalised using the following protocols:

• The minimum polygon size has a maximum axis length of at least 10 m.

• Where habitat boundaries are obscured by shadow, then the start of the shadow is taken as the habitat boundary. i.e. any shadow is not included as ‘saltmarsh habitat’.

• Saltmarsh habitat separated by distinct geomorphological features (e.g. channels) was digitised as separate polygons, even if the distance between the habitats is less than 10m.

These methods are the same as those used to map saltmarsh habitat in Bay of Islands, Whangarei and Bay of Islands.

The attribute table contains the author of each polygon ‘Author’, the name of the aerial image used ‘Aerial’, the date the aerial image was flown ‘Date_Flown’, and the area of the polygon in hectares. These were compulsory attributes. The attribute table also contains three optional attributes: ‘Confidence’; ‘Comments’; and ‘Verified’. Confidence is the authors confidence that the polygon they created is in fact saltmarsh rather than another similar feature e.g. algae or rocks. The only values to be entered in this field were ‘low’, ’moderate’and ‘high’. Comments are an open field for the author to write any comments about the polygon they have created. The column ‘Verified’was used if a saltmarsh polygon has been confirmed with a visual observation by a staff member of the Northland Regional Council. The name of the staff member was entered in the column. A verified polygon does not mean that the shape or size of the polygon has been verified. It means that the presence of saltmarsh at that location has been verified.

Before the layer was finalised, the entire Northland coast was checked by Richard Griffiths. The purpose of this QA was to ensure that all saltmarsh habitats had been identified, and that the attribute table had been completed accurately.

Version 1 July 2015