Describe types of Charts and Diagrams. Differentiate between Line Chart

Describe types of Charts and Diagrams. Differentiate between Line Chart, Bar Chart and Histogram.

Ans.

The various types of charts and diagrams used in data analysis are discussed below:

(1) One-Dimensional Diagrams

Bar diagrams are the most common type of diagrams used in practice. A bar is a thick line whose width is shown merely for attention. They are called one-dimensional because it is only the length of the bar that matters and not the width. When the number of items is large, lines may be drawn instead of bars to economise space.

While constructing the bar diagram, it is desirable (though not necessary) to write the respective figure at the end of each bar so that the reader can know the precise value without looking at the scale. This is particularly so where the scale is too narrow, for example, 1′ on paper may represent 10 crore people.

These diagrams are in the form of bar or line charts and can be classified as:

(i) Line Diagram: Line diagram is used in case where there are many items to be shown and there is not much of difference in their values. Such diagram is prepared by drawing a vertical line for each item according to the scale. The distance between lines is kept uniform. Line diagram makes comparison easy, but it is less attractive.

(ii) Bar Diagram :

(a) Simple Bar Diagram: A simple bar diagram is used to show only one variable, for example, production, wages, sales, etc. The values of the variable may relate to different years or different items. For example, production of sugar over a few years in a single country,. or production of sugar in different countries can be shown with the help of this diagram. The bars are arranged in time sequence or the size of the variable. The length of each bar depends upon he size of the items. Such bars are very simple to construct and understand. Hence they are popular. But their greatest limitations is that only one category of data can be shown.

(b) Multiple Bar Diagram : In this type of diagram two or more bars are constructed, adjoining each other, to represent either different components of a total or to show multiple-variables. The bars are grouped together, making it possible to draw more than one set of comparisons. The length of each bar will be in proportion to the magnitude to be represented As in the case of a simple bar chart, there should be a gap between the vertical axis and the first bar. However, the total bars of one set have to be continuous. The gaps between the different sets of bars is to be identical. This diagram is useful either when the number of related variables is more than one or where changes in the actual values of the component figures are significant. To distinguish between the different bars in a set, different colours, shades, dotings or crossings may be used and key or index to this effect may be given.

(c) Sub-Divided Bar Diagram: A subdivided diagram is prepared when the different components of a total the given. The bars are sub-divided into component parts. In general sub-divided or component bar diagrams are to be used if the total magnitude of the given is to be divided into various parts or sub-classes or components. First of all a bar representing the total is drawn. Then it is divided into various segments, each segment representing given components of the total. Different shades or colours, crossing or dotting, or designs are used to distinguish the various components and a key or index is given along with diagram to explain these differences.

In addition to the general rules for constructing bar diagrams the following points may be kept in mind while constructing sub-divided or component bar diagrams. (i) To facilitate comparisons the order of the various components in different bars should be the same. It is customary to show the largest component at the base of the bar and the smallest component at the top so that the various components appear in the order of their magnitude. (ii) An index or key showing the various components represented by different shades, dotting, colours, etc. should be given. (iii) The use of sub-divided bar diagram is not suggested if the number of components exceeds 6, because in that case the diagram is loaded with too much information and is not easy to understand and interpret. Pie or circle diagram is appropriate in such a situation.

(d) Percentage Bar Diagram : Subdivided or component bar diagram presented graphically on percentage basis gives percentage bar diagrams. They are specially useful for the diagrammatic portrayal of the relative changes in the data. Percentage bar diagram is used to highlight the relative importance of the various component parts to the whole. The total for each bar is taken as 100 and the value of each component or part is expressed, as percentage of the respective totals. Thus in a percentage bar diagram, all the bars will be of the same height viz., 100, while the various segments of the bar representing the different components will vary in height depending on their percentage values to the total. Percentage bars are quite convenient and useful for comparing two or more sets of data.

(iii) Histogram: The histogram is a summary graph showing a count of the data points falling in various ranges The effect is a rough approximation of the frequency distribution of the data. The groups of data are called classes, and in the context of a histogram they are known as bins, because one can think of them as containers that accumulate data and “fill up” at a rate equal to the frequency of that data class.

The histogram should be clearly distinguished from a bar diagram. The distinction lies in the fact that whereas a bar diagram is one-dimensional, i.e., only the length of the bar is material and not the width, a histogram is two-dimensional, that is, in a histogram both the length as well as the width are important.

A histogram cannot be constructed for a distribution with open-end classes. Moreover, a histogram can be quite misleading if the distribution has unequal class-intervals and suitable adjustments in frequencies are not made.

(2) Two-Dimensional Diagrams

In one-dimensional diagrams, only length is taken into account. But in two-dimensional diagrams the areas represent the data and so the length and breadth have both to be taken into account. Such diagrams are also called area diagrams or surface diagrams. The important types of area diagrams are:

(i) Rectangles: Rectangles are used to represent the relative magnitude of two or more values. Rectangles are placed side by side for comparison. When two sets of figures are to be represented by rectangle, either of the two methods may be adopted.

(a) Percentage Sub-Divided Rectangular Diagram : In such a diagram the widths of rectangles are kept according to the proportion of the values and, the various components of the values are converted into percentages and the rectangles divided according to them.

(b) Sub-Divided Rectangles: Such diagrams are used to show three related phenomena. Per unit cost, quantity of sales and sales revenue can be shown with the help of such a diagram.

(ii) Squares: The rectangular method of diagrammatic presentation is difficult to use where the values of items vary widely. The method of drawing a square diagram is very simple. One has to take the square root of the values of various item that are to be shown in the diagrams and then select a suitable scale to draw the squares.

(iii) Pie Charts: The pie chart is presented in a circle dividing the charts in different components according to the needs of the distinctive data. The slices of the circle a re also noted with the name and their percentage shares in the total circle. The slices are divided according to the proportion of their shares in the 360°. This proportions are, therefore, calculated in accordance with the number of degrees of each angle of the slice.

(3) Three Dimensional Diagrams

A diagram is two-dimensional geometric symbolic a representation of information according to some visualization technique. Sometimes, the technique uses a three-dimensional visualization which is then projected onto the two-dimensional surface.

(4) Pictograms and Cartograms

The pictograph uses tiny pictures or symbols to represent the idea or subject. This device is used to give a more vivid picture of the report. It is appropriate for bar-type charts. It is not intended for detailed study and precise measurement, but to give one short glimpse of the findings.

A cartogram is a map in which some thematic mapping variable such as travel time or Gross National Product-is substituted for land area. The geometry or space of the map is distorted in order to convey the information of this alternate variable. There are two main types of cartograms area and distance cartograms.