Required Data, within the Main Window of DatMapR, defines the Project database field on which the map will be based, and any selection required to define the sub-set of records to be used.
Field to be mapped shows a pull down list of the field names defined for the current open project. By default the first field is selected.
Records can be selected using up to four constraints (Select where ... and ...).
Each constrain consists of …
a field name selected from a pull-down list (the top ‘blank’ entry effectively omits that constraint),
an operator (‘=’,’>=’,’>’,’<=’,’<’,’<>’ (not equal),’=~’,’Like’) again taken from a pull-down list, and
a comparison value.
If the project is based on OS NGR, 'NGR Precision' is added as an extra option on the list of field names. This allows the user to select on the precision of data records imported as OS NGR strings (e.g. NGR Precision <=1 will select those at 1km or finer precision (e.g. SK1234, SK123456, but not SK12 or SK12T)
The operators '=~' and 'Like' allow further flexibility in the selection when using text fields. For Numeric fields they are treated as ‘=’
'=~' compares only the leading part of the field (e.g. Species=~Cygnus will select any species of swan (e.g. Cygnus olor)).
'Like' allows further flexibility by allowing 'wildcard' characters in the comparison value - 'underscore' ('_') ignores a single wild character, and 'per-cent' ('%') ignores any number of wild characters
(e.g. ‘A_M’ would match ‘AXM’ but not ‘AM’ or ‘AXYZM’,
‘A%M’ would match ‘AXM’, ‘AM’ and ‘AXYZM’.
Species Like Cygnus% has the same effect as Species=~Cygnus).
You need to note that multiple constraints are combined by an ‘and’ operator. Hence records will only be selected where they satisfy all of the defined constraints.
Location=Sheffield AND Location=Chestefield
will select no records since the Location field cannot satisfy both cnstraints.
Location=Sheffield AND Year>=1990 AND Year <2000
will select those records with the required Location and the required Year range (1990-1999).
These selection constraints can be made to ignore the case of text fields using the Ignore Case tick-box. This affects the treatment of text in the selection of records and in the definition of Data Bands. Note that when Ignore Case is selected, text values in some messages may be shown as UPPER CASE even where the Data is held as Mixed Case. The stored data is not affected, and the Ignore Case tick-box can be 'toggled' as necessary.
