Why do some locations not appear on the trend map, although a time series plot is available?
For a trend value to be calculated, that location must hold valid index data for at least 80% of the period for which the trend is calculated. For example, for a trend period 1901-1999 (99 years), at least 80 years must have valid data. Also, the homogeneity test result for the underlying series must be ‘useful’ or ‘doubtful’ for this period. If the test result is ‘suspect’ or less than 80% of the trend period holds valid index data, the trend for that location is not calculated and therefore not plotted on the trend map. A time series plot is produced if any valid index data is available for the location in question, with the only restriction that index values for an individual year are only calculated if no more than 3% of the days are missing.
