Scale indicators are used to illustrate distances within the map so that viewers can understand the size of the space displayed and infer the distance between features in the map. The scale indicators comes in three forms a scale bar, ratio and measurement.
The image above shows the three types of scale indicators scale bar above left, ratio above middle and measurement above right.
The scale bar is used to show the size of the subject and enables to viewer to infer and understand the distances between features on the map.
The ratio scale will indicate the relative proportion of the map in relation to the real-world. So we might have a ration of 1:50000 (“one to fifty-thousand”) which means that for each unit of measurement on the map it equals 50,000 of the same unit on the surface of the Earth. So one inch on the map equals 50,000 inches on the surface of the Earth, one centimeter on the map equals 50,000 centimeters on the surface of the Earth, and one foot equals 50,000 feet on the surface of the Earth and so one.
The measurement scale will indicate a standard unit of measurement in relation to another standard unit like inches to miles, centimeters to kilometers and so on.
It is important also that you have chosen the correct projection for the map as well, because the scale indicator in calculated automatically from the projection. If the projection is incorrect or there is something else wrong with it, then this will be reflected in the scale bar which will give the wrong dimensions for distance.
General Rules for Scale Indicators
For most purposes a single scale bar at the bottom of the map document is satisfactory. A well developed map might employ two or three types of scale indicators, and some times different units of measure to make it intelligible to a wider population. For example in the image below, taken from an old USGS topographic map, we can see the ratio scale along with scale bars in imperial and metric units:
The scale bar should take up about one-quarter to one-third of the total width of the subject, and often appears near the bottom in the middle of the document. Here is another detail form the USGS topographic map showing the location of the scale indicators:
When using a ratio scale it is a good idea to set the scale to a relatively “round” number like 1:50000 or 1:24000. If possible please avoid a scale like 1:814536, which, while mathematically sound, is just too “busy.”
Similarly when using a measurement scale make sure that the units are from the same system and that the value of the units are a round number so that you will have "1 inch equals 2 miles" an not "1 centimeter equals 2.34492 miles" or "1 inches equals 2.34492 miles."
North arrows are a self-evident and straight-forward component of maps. Their purpose is to indicate the direction of the north pole from the subject of the map.
Despite their straightforward nature, the north arrow makes some assumptions that can be quite contentious. According to some scholars orienting a map with north at the top might reinforce preferences for northern locations and biases against southern locations. This topic comes to the fore in debates about the “Global South” and the implications of poverty and under-development that attend countries around the tropics and southerly latitudes. Sometimes even within a country like the United States or Italy the southern regions might be caricatured by poverty and under-development. Also, reorienting a map with the south at the top like the “McArthur's Universal Corrective World Map” is designed to challenge the viewers assumptions about the world.
Never-the-less ArcMap only comes with north arrows. There are nearly 100 different types of arrow to chose form differing from each other mainly in ornament.
The image above shows some examples of the different types of north arrows available in ArcMap.
General Rules for North Arrows
The North Arrow should be placed in the lower part of the map document. The lower corners are often a good place to put north arrows like the ones shown in series 1 to 6 in the image above. Though sometimes it might be placed near the middle. A vertical north arrow like those shown in series 25 to 30, above, might get "lost" in the confusion of a visually intensive map.
In the image above, from a detail of a USGS topographic map, the vertical north arrow is quite effectively placed in the left-of-center position, with wide margins around it to prevent crowding. This north arrow is actually a composite of the geographic north and the magnetic north which is slightly to the north-west.
In any event the north arrow should be placed in the same area of the document as the scale bar and other information about the map and not floating around by itself.
It is argued here that a simpler north arrow is more "professional" looking and the type of arrow seen in series 16 to 20 (repeated below), should be reserved for novelty maps or maps of a historical interest. It is a matter of preference, however.
In addition to the north arrow, legend, scale indicator, etc., a completed map will have information about the projection used, the datum, the data source, and the author.
An example will look like this:
General guidelines for adding information:
It is not always necessary to add these information. For example if you are publishing a series of maps within the columns of an article that show demographic changed over time, for example, then you do not have to add this information for each map. It will likely be impossible to see when published anyways.
However for a stand-alone map or one published in a book that takes up a whole page this information is necessary to understand the currency reliability authority and purpose of the map.
