序数比例尺

• d3.scale.ordinal - construct an ordinal scale.
• ordinal - get the range value corresponding to a given domain value.
• ordinal.domain - get or set the scale's input domain.
• ordinal.range - get or set the scale's output range.
• ordinal.rangePoints - divide a continuous output range for discrete points.
• ordinal.rangeRoundPoints - divide a continuous output range for discrete points.
• ordinal.rangeBands - divide a continuous output range for discrete bands.
• ordinal.rangeRoundBands - divide a continuous output range for discrete bands.
• ordinal.rangeBand - get the discrete range band width.
• ordinal.rangeExtent - get the minimum and maximum values of the output range.
• ordinal.copy - create a new scale from an existing scale.
• d3.scale.category10 - construct an ordinal scale with ten categorical colors.
• d3.scale.category20 - construct an ordinal scale with twenty categorical colors.
• d3.scale.category20b - construct an ordinal scale with twenty categorical colors.
• d3.scale.category20c - construct an ordinal scale with twenty categorical colors.