TOPOGRAPHICAL MAP INTERPRETATION (PHOTOGRAPHS OVERLAPING, PHOTOGRAMMERTRY, MAP MAKING AND DIAGRAMS SKETCHING)
PHOTOGRAPHS OVER LAPPING
It becomes difficult for a single photographic view as a respective photograph to cover the very huge part of land space at once. Following this difficult several successive photographic views as well as photographs can be produced to make the whole huge part covered.
Then the different successive photographs taken along the same or different photos to appear on the same photo. This photographic technique is referred to photo over lapping or photo mosaic.
Thus; photo overlapping is the photographic technique of two or more successive photos combined and appear as one photo.
Is the technique of making the ground that party appears on the different successive photos appear on a similar photographic by combining the different successive
There are two types of the photo over lapping namely
- Forward photo overlapping.
- Side photo overlapping.
1. Forward photo overlapping.
Forwards photo overlapping is made by combining two or more successive photos taken along the same flying height line.
2.Side photo overlapping.
Side photo overlapping is made by combining the top and bottom parts of two different successive photographs taken along different flight lines.
Photographs are used to asses the geographical facts including the measurements of the geographical features measurements like area size and distance is known as photogrammetric.
How ever; photo gram metric does not stick only on measurements determination; it also involves the assessment of other geographical facts.
Photogrammetric is made possible only on vertical aerial photographs as whose scales less distorted.
Distance refers to a length of an elongated object or an interval between two parts on the earth’s surface given in linear measurement units.
The distance of any features is determined as follow.
·Photo scale consideration.
· Measure the photo distance of the object. If the elongated objects is straight, a ruler can be used. But if the objects is not straight, a divider, a piece of paper or thread can be used.
· Convert the photo distance into actual distance by regarding the photo scale.
Area size means the extent f coverage or bigness of a feature on the earth’s surface given in unit square.
The area of any feature is determined as follow:-
· Photo scale consideration.
· Examine the appearance of the feature on the photo.
If the figure is regular apply more directly the relevant mathematical formula with respect to the shape of the figure. Is considerably irregular, divide it into a convenient number of the mathematical figures, and then calculate the area size of each figure.
SKETCHING OF MAP FROM THE VERTICAL AERIAL PHOTOGRAPH
Drawing of a map from the vertical photograph should follow the following procedure.
1. Examine carefully the given photograph. If possible use the stereoscopy to get the more clear view of the objects.
2. Take a trace paper and over lay the photograph.
3. Separate the features of the photograph on the trace paper by producing the fine lines. This has to take into consideration the textures of the objects.
4. Provide the distinctive shade on the trace paper to have clear distinction of the features on the map.
5. Develop the map more clearly and associate it with important supportive details to make it well defined. The supportive details include; title key, north direction, scale and other important thinks.
6. The map sketched is of the same size with photograph. It can be further develop by being enlarged or reduced.
SKETCHING OF DIAGRAMS
A map can be only sketched from the vertical photographs. From the horizontal and oblique photographs, diagrams can be sketched to provide visual impression of the features described from the photograph.
To draw diagram from photograph, the steps given below should be followed.
1. Draw a frame work of either rectangle or square on piece of paper. The frame work should be proportional to the size of the photograph. Keep this paper aside.
2. Subdivided the photograph from which a diagram to be drawn into three equal sections by faintly drawing horizontal lines a cross the photograph use pencil to develop foreground, middle ground and back ground.
3. Transfer the details from the photograph into the frame work of the diagram.
4. Start by inserting details in the back ground as it appears on the photograph.
5. Fill the details in the middle ground and finally put in the important features in the foreground. The square drawn on the photograph guide in placing the various features in their rights positions.
6. The sketch should be completed by drawing and labeling all the important features such as vegetation, land use, prominent buildings, transport and communication and then; give a suitable title of the sketch.
USES OF PHOTOGRAPHS
Photographs are produced purposely to meet certain objectives, and these are what considered as the uses of photographs. Some of the considerable uses of photographs include the following:-
(a) They are used for map making in a number of ways as follows.
They make confirmation of the details to be surveyed in an area to be mapped.
They can be used for preliminary mapping of areas
They are used for rapid survey of the remote areas which can not be reached.
(b)Photography’s provide the basis for making geographical description and analysis. It is thus; photographs make people to understand the geographical details of areas represented.
(c)They are used for making resources assessment more particularly of areas that can not be easily reached. For instance; assessment of plant species, wild animals and others.
(d)They are for military purposes and mostly used for doing reconnaissance in war.
(e)Photographs are used for making measurements assessment of the geographical features particularly for areas that are not easily reached. The assessment can be on distance, size and height.
(f)Photographs are used for engineering works. i.e. they give significant information that can be used to provide good basis in designing engineering structures.
(g)Photographs are used to make storage of instant data of like; graduation, weddings, meeting. Family celebrations and others.
(h)They are more applied for field investigation.
Strengths of photographs in geographical studies
Photographs permit observation of the wider area of interest at the same time.
They are not selective as show everything that visible. i.e. they show all details of the particular area photographed as the camera does not select. Hence; photography provides a mass of details of an area captured.
They display the absolute appearance of objects in true image as appear in real life.
They provide the basis for geographical description and analysis of the photographed area.
They provide easily instant data about an object for instance; the occurrence of floods, people, gathering, cars congestion etc.
They give quick information of the required feature, as it can be compared to other sources. This is attained as a photograph takes a short period of time to be produced. For instance; photograph of an object can be produced within three minutes. Beside to this, they are less expensive to be produced
Photographs particularly vertical aerial photos are used for map making.
Limitations (setbacks) of photographs
Sometimes, photographs give un required details as the camera recording images on films are not selective. i.e. they provide mass details some of which are not needed in the analysis.
They give wrong impression on the size of objects. A big object on a photograph may look apparently larger. Hence people, who are not familiar with the objects observed on the photograph, develop wrong idea into their mind about the size of the objects.
Photographs are subjected to a problem of scale distortion. i.e. the ration of distance to ground is not uniform all over the photo, as it gets progress silvery smaller from the fore ground to back ground or from the centre to out wards. Hence; it is difficult to judge the used photo scale. How ever; the degree of photo scale distortion is much higher on horizontal and oblique photographs; and it is less enough on the vertical photographs.
Not all objects of the landscape can be easily seen on the photograph because of being hidden by other objects.
Photographs do not show clearly the major directions of the photographed area.
It is far more difficult to determine accurate measurement of the geographical features from the photograph, as the scale is not constant. It is thus; the measurements of the objects from the photographs particularly the horizontal and oblique photographs given on the estimation basis.
Similarities and differences between photographs and maps
Geographical studies area partly enhanced by photographs and maps. i.e. both have similar role towards geographical studies and they are considered being reliable geographical tools. It is there fore important to understand how the two geographical tools appear similar and contrast.
Both are subjected to scale as are much smaller in size compare to objects visually represented which are much large in size. i.e. they have considerable relationship of distance to the large objectives represented.
Both give land details in terms of natural and man made features as they make representation of areas in which the features are present. Hence; provide good basis for making analysis and description of the geographical features.
Both make visual representation of land details on flat bodies mostly the pieces of paper.
Both show position location of the features. On maps are shown by methods of place naming, grid reference, bearing and latitudes and longitudes; while on the photograph are shown by pointing out the important parts of the photography where the objects found like; foreground, middle ground, back ground, left, right, fore right etc.
Both show the features of landscape in three dimensions. i.e. The features on maps or photograph displayed with their height, length and width.
Maps are selective as do not show all details of the represented area; while photographs are not selective as all details of the focused areas appear.
Maps make uniformity coverage of the ground; while, photographs do not make uniformity cover age of the ground.
In connection to the above point, map scale is constant. i.e. the ration of distance on the map to the ground is constant; while the scale of a photograph changes by getting progressively smaller from the principle point to outwards on vertical air photographs; or from the foreground to background on ground and oblique photographs.
Photographs show objects of the earth’s surface on true image as appear in real life; while maps shows earth’s surface objects by means of conventional symbol and signs which normally described in the map key
Photographs particularly the vertical aerial photographs, are used for map making while, maps are not used for photograph production.
Photographs take short period of time and less expensive to have been produced as it can be compared to maps.
Maps show north direction while photographs do not give.
Map interpretation is comparatively difficult; while the interpretation of the photographs not difficult as features displayed on true image as appear in real life
TYPES OF INFORMATION FROM PHOTOGRAPHS
Photograph interpretation is an art of examining a photograph to reflect the geographical facts of the respective photographed area. It is done by identifying and translating the features seen on the photograph to the real situation
Photo interpretation has to do with two important processes:
Photo reading is the art of examining and identifying the images of as appear directly on the photo. While photo analysis is a process of translating the features seen directly on the photo to other geographical facts. However; interpretation techniques of the photographs differ depending on a type of a photograph the photo user has been given.
Interpretation of ground and oblique photographs
Interpretation of the ground and oblique photographs is comparatively easier as objects on such photographs clearly observed. However; perfect skill for interpreting these photographs requires constant practices and wider geographical knowledge.
Interpretation of these photographs should involve the two basic processes of photo reading and photo analysis. By photo reading; objects on the photo in all sections are recognized.
This is done directly by naked eyes as the objects clearly observed on the photograph. In photo analysis, the recognized features are related to other geographical facts for description, explanation or suggestion.
For instance; with the presence of sisal on the photograph, the interpreter may judge that the area receive moderate amount of rainfall as the crop requires such a condition of water supply.
Interpretation of Vertical aerial photograph
The perfect skill for interpretation of the vertical aerial photographs also requires constant practices and wider geographical knowledge. It involves the same basic processes to other forms of photographs of the following;-
Photo reading; which is relatively to the identification of the objects that observed on the photograph.
Photo analysis; it is about the translation of the features recognized on the photographs to other geographical facts which might not appear directly on the photo. Photo reading is dote by the use of naked eyes directly or with the use of the special device called stereoscopy.
By the use of naked eyes, enable the photo user to observe only flat views of the objects on the photo. But with the use of stereoscopy, the objects on the photo are magnified and enable the user to view the features more clearly in three dimensions by getting, their height, depth and width.
However as the objects clearly observed by the naked eyes, the interpretation of the vertical aerial photographs is aided by considering some guiding techniques based on the characteristics of the features on the photo in terms of appearance.
These are what also understood as elements of the vertical photographs and include the following:-
It is about layout (spatial arrangement) of observable objects on the photograph with reflection to the actual area. Consideration of patterns help to recognize features and translated to other geographical facts. For instance; the pattern of the rivers on the stand the nature of relief and rocks. E.g. radial pattern if observed gives an impression that the area has rocks of uniform hardness. Scattered settlements may make people to understand that, people engage in animal keeping or scattered cultivation.
Shape refers to the general from, structure or outline of individual objects on photo and up on the area or the regularities of the objects on the photo and up on the photographed area. This is basically helps to recognize natural and man made features. Usually regular shape indicates man made features, while irregular shape indicates natural feature. For instance; if vegetation on the photograph observed regular, reflects that, the vegetation is of planted trees.
Texture refers to the shade pattern or smoothness and coarseness of objects on the photograph. Some objects on the photo like that of vegetation display a shade pattern which can be course or light. It is thus; the consideration of the objects textures on the photograph in relation to other consideration helps to reveal the size and concentration of objects on the photo and up on the area. For instance if plants on the photograph observed to have course texture impress that the vegetation is of closely big trees.
Colour refers to the relative brightness of objects on the photograph. Commonly objects on the photo display colours and the common colours are of either dark or light especially on the black and white print. The colours have reflection to certain objects. For instance the dark coloured objects on the photo may reflects a road dense forest etc; while lighter colour reflects railway, grassland etc. But to recognize specific object, it requires other considerations of the objects on their pattern, texture, shape etc. e.g. the dark coloured liner object reflects a road.
Association takes into account of the relationship between features in an area. It has to bear in mind that, some objects are always found in association with others. It is thus; the identification of features that one would expect to associate with other features may provide a clue about other objects. For example the presence of ox bow lake reflects the presence of a flood plain as such associated in a food plan.
If the location of a photographed area is recognized the person who likely to realize other facts which also present in the area. The location is revealed by considering the feature present on the photograph.
It is about apparent bigness of the features on the photograph. The consideration help to recognize size of photographed area and relative photo scale size. For instance; if objects appear bigger on the photo; make reflection that smaller area covered and the photograph has large scale. Conversely; if objects appear much smaller impress that; wider area covered the photograph subjected to small scale.
Back ground information.
If all attempts to identify objects have field, the user of photograph must then refer to maps and written descriptions of the area.