Most construction planning and scheduling is undertaken using Bar charts (also known as Gantt charts), and for all but the smallest of jobs this invariably means using a software planning package such as Microsoft Project or Primavera P6. 

Planning tools are primarily communications tools, the programme never fixed any steel or placed any concrete. The programme is there to communicate what needs to be done, when and to illustrate any problems so that the people who actually do the work can do so in an efficient manner. 

Bar charts plot activities against time and so are “Time Activity” charts. This is excellent when you need to know what to do at a specific time, but in many projects what you do at a specific time is often far less important than where you are doing it. Even more important, are you trying to do two things in the same place at the same time? This is particularly true of linear projects such as pipelines, railways, tunnels and roads, as it is of repetitious projects such as house building or high rise building. 

For these types of projects, a means of showing the activities against Time AND Location is needed and this is achieved by the use of a Time Location Chart. 

A Time Location Chart plots Time on one axis of the chart, and Location (distance) on the other, with the activities being shown as a line or shape in the main body of the chart. It is therefore simple to be able to view what activity and in what location it is occurring at any particular time. 

In the simple example above; on the 11^th March the Temporary Fencing should have reached 8000, while the Topsoil strip should be at about 3000 on the same date. 

If we now add in some progress to the 4^th March;

It is easy to see that if we start the top soil stripping as planned and progress as planned, then we will hit a problem at about 6000, because the fencing will not be ready for the topsoil.

This is very easy to see on a Time Location chart, but very difficult to tell from a bar chart. Clashes of this nature can be spotted almost instantly on a Time Location Chart but can be almost impossible to see on a conventional bar chart or even on a 4D BIM model. 

Unlike a bar chart where the layout of time on the horizontal axis of the page and the activities on the vertical axis is almost universally adopted, the exact format of a Time Location Chart is far less fixed. Usually in a time location chart, location (distance) is on the horizontal axis and time on the vertical, although whether the earliest date is at the top or bottom of the chart is far more variable. In the UK charts for Roads and Tunnels typically start at the top and work down, where as pipelines and buildings tend to start at the bottom of the page and work up. 

Because on cross country projects the location is a distance (chainage), this type of chart is often referred to as a Time Distance chart or a Time Chainage chart, in building it is often referred to as Line of Balance. 

In order to clarify the chart often a location drawing, schematic or map is shown above the location along with other useful information.

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