It seems like you may require a 'scale break' feature, which is currently not supported by Highcharts.
An alternative solution is to set a rounded value and utilize a different property for the point to display in the tooltip: http://jsfiddle.net/4NV2J/6/
Another option is to incorporate label.formatter
for the yAxis, enhancing the readability of the chart.
Here is the code snippet:
$('#container').highcharts({
chart: {
type: 'spline'
},
title: {
text: 'Y axis'
},
xAxis: {
categories: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
},
yAxis: {
tickInterval: 1,
min: -1,
max: 6,
title: {
text: 'Value'
},
labels: {
formatter: function() {
if(this.isFirst) {
return '< 0';
} else if (this.isLast) {
return '> 5';
} else {
return this.value;
}
}
}
},
tooltip: {
pointFormat: '<span style="color:{series.color}">\u25CF</span> {series.name}: <b>{point.options.trueValue}</b><br/>'
},
series: [{
data: [{
y: 3,
trueValue: 3
}, {
y: 4,
trueValue: 4
}, {
y: -1,
trueValue: -4
}, {
y: 6,
trueValue: 40
}]
}]
});