Wiggle is a simple text file format showing the value of a particular characteristic at a point, so basically just a bar chart let loose to represent anything your imagination can think of. There are 3 types of wiggle files : fixedStep, variablStep and BedGraph.
so as the name says the step is fixed . What is a step ? well simply put the distance between 2 adjacent bars is the step.
fixedStep chrom=chrN
start=position step=stepInterval
[span=windowSize]
dataValue1
dataValue2
but what if all of my data is not at the same uniform distance from each other ? welcome to variable step where width of bars ( span is fixed ), but the step can be specified
variableStep chrom=chrN
[span=windowSize]
chromStartA dataValueA
chromStartB dataValueB
then comes the most flexible wiggle where the bars can be any width wide and can be spaced any distance apart from each other.
chrom chromStart chromEnd dataValue