Raster File Setup

This page describes the raster file setup screen which allows raster files to be created and edited and is reached from themain form when the new', import or modify buttons are pressed and the raster option selected. There will be differences in the appearance of the frame, according to which button was pressed and the contents of the existing file for import and modify.

There are two main sections: Map scaling text boxes and Habitats and habitat groups tables.

Map scaling text boxes

Width (no. cells), Height (no. cells)

These determine the size of the raster map in terms of the number of cells it will contain. These boxes are greyed out for import and modify because the size of the map is defined by the number of rows and columns in the existing files. In new mode, they may be edited, in which case the values of E and N will change (to E = W + (width * coord units) & N = S + (width * coord units) ).

Units Per Cell

This determines the size of each cell in terms of coordinate units. Note that if you change this the values of ‘E’ & ‘N’ will change as indicated above.

W, S

W & S determine the coordinates of the left, lower corner of the map. Changes to these will also cause changes in E & N.

E, N

E & N are the coordinates for the right, upper corner of the map. These text boxes are not editable (as indicated by their grey colour), but the values can be changed by altering any of the other text boxes.

Scale Of Coordintae Units

This allows the coordinate scale of the map to be altered. Note that this is different from coordinate Units Per Cell which determines the dimensions of each raster cell in the number of coordinate units.

Habitats and habitat groups tables

These determine how the cell values stored within the raster map are converted into habitats for display and analysis. The system will take a little bit of learning, but once that is done is very powerful, allowing habitat classifications to be changed easily for different analyses.

The system consists of Habitats and Habitat Groups. Each habitat is represented by the same value wherever it occurs in the map and has its own label. Each habitat may belong to one Habitat group. Each habitat group has a colour (which is used in the the main window map, and in Habitat Analysis options) and a label which is made up from the labels of its constituent habitats. The habitat group is the classification used in Habitat analysis – so for example the contents of a range will be analysed in terms of habitat groups (however if you have just one habitat per habitat group this is equivalent to using habitats themselves). This allows for great flexibility in altering habitat classifications for different analyses, without having to alter the raw data in the map itself.

Habitats

Click in the habitat column to alter the label for individual habitats.

Click in the group column to alter the habitat group that a habitat belongs to.

Use the add habitat button to add new habitats.

Habitat groups

Click in the colour column to alter the colour assigned to a habitat group.

Use the add group button to add new habitat groups.

The label given to each habitat group is set from its constituent habitats. If there is just one habitat in the habitat group the labels will be the same. For any additional habitats, the habitat group label will be constructed as follows :

Label1+MapValue2+MapValue3…+MapValueN

This provides a unique label whilst minimising the number of characters. Labels with greater than 11 characters may obstruct the map display in habitat analysis options.

Quick Tip

When creating a new file, first add all of the desired habitat groups (the right hand table), then add single habitats (the left hand table). For each habitat, the habitat group will be set automatically, to the same number as the habitat or to the highest habitat group if that is lower.

Constraints

A number of constraints are placed upon the choice of habitat groups and colours:

• The colour for cell value 0 is always black, and cannot be edited.
• There are currently a maximum of 49 habitat groups (+ 0 for no data)
• The colour of the 49th habitat group is set to white and cannot be edited.
• No two habitat groups may have the same colour.
• No other habitat group than 0 may have the colour black, and no other habitat group than 49 may have the colour white.
• Map values must be sequential integers starting at 1.