Reference timeline

A reference timeline plot reference by reference year, that is, by the year corresponding paper was published. This kind of timelines are useful for two purposes:

1. Identification of load knowledge. Normally the year of emergence of a specialty is well-known. References that appear on the reference timeline from before the specialty emergence represent loan knowledge concepts from pre-existing specialties.
2. Identification of emerging discoveries and 'hot' concepts. Highly cited references that appear in the last year or two of the dataset represent very recent papers that are attracting a lot of current attention in the specialty. Thus, they represent 'hot new concepts'.

Generating the reference timeline

• Before a reference timeline can be generated, you must first perform co-citation clustering.
• On the TFGUI window, select Coccurrence > make crossmaps > reference timeline. This will produce a separate window containing the reference timeline.

Description of the reference timeline

• The elements of the reference timeline are shown in the figure below:

1. Plot area.  The x position of each circle corresponds to a reference on the dendrogram, the y position of circle is the year of publication of the paper corresponding to the circle's reference.  The size of the circle is proportional to the number of times that the reference has been cited.
2. Reference year axis. Years increase going up.
3. Cocitation clustering dendrogram.  The dendrogram is identical to the RF to reference crossmap dendrogram.
4. Reference labels. Reference labels are identical to the RF to reference crossmap labels.
5. Crosshairs. Clicking the mouse in the plot area put a vertical and horizontal line on the plot that intersects at the point that was selected.  This crosshair is useful for identifying the research front and reference of selected circles on the map.
6. Annotate menu.  The menu has functions to increase or decrease the circle sizes, zoom to interesting parts of the map, and to adjust plot margins.
7. Webpage menu.  This menu has a control to generate a reference timeline webpage that can be posted to a web server.