Instructor's kit for O-mapping courses - Survey Notes / Survey Draft

Instructor's kit for O-mapping courses
Survey Notes / Survey Draft

Introduction

Survey notes are made directly on to a copy of the base map or on to one, two or three separate polyester sheets overlaying the base map. With two or three sheets, survey information is split between:

landform features and rock details
man made features and water features
vegetation

Using three sheets may cause difficulty in reading the base map unless the film is very thin.

At the end of the survey session the information is transferred on to either a master survey draft or directly into the computer.

The survey draft

This is the up to date drawing of survey results from all sources from which the final map will be produced. The survey draft is both a record of survey and a clear presentation of the information for the final map. The way it is presented depends on the intended method of drawing: using a computer, pen and ink or scribing.

All line thicknesses on the draft should be scaled proportionally to the line thicknesses on the final map. This shows up any problems of displacement made necessary by drawing with thicknesses greater than the space taken up by the feature on the ground. Such problems should be resolved at this stage rather than at the final drawing. Where there is considerable density of detail, care should be taken to maintain legibility. It should be remembered that legibility increases when several colours are used rather than just a single colour.

One or more sheets - the survey draft is drawn on to one or more sheets depending on the complexity of the line work and method of cartography. When using more than one sheet, the line and point detail are drawn on seperate sheets to that containing the screen areas.

Lines and Areas - Ink pens (0.25 / 0.35 / 0.50 and 0.70 in black, red and blue) and black lead pencil are used for drawing lines and point features while coloured pencils are used for screen areas on the survey draft. Which are used and for what is dependent on the complexity of the map and method of cartography.

Colours - the colours used depends on the type of terrain, the most important detail being drawn in black. Thus maps with complex contours the following should be used:

contours: black
lines and points: red

and for maps with detailed vegetation and many line or point features

contours: red
lines and points: black

Drawing line and point features in red has the advantage for the cartographer using pen and ink methods in that on the final drawing all the red lines must be covered.

The colours of the vegetation / open land / stony ground should be chosen to be as different as possible and it should be possible to show different shades in combination.

If the survey draft is drawn very clearly and in the correct dimensions, it can be used afterwards for corrections. A reduced colour copy may also be useful for initial course planning.

Survey draft for scanning

The complexity of the line work, whether auto tracing software is being used and the quality of the scanner (monochrome or colour and resolution) will determine whether the survey draft is drawn with one or more sheets. For simple areas or when using a high quality colour scanner without auto tracing a single sheet is sufficient. When using monochrome or low resolution scanners a multi sheet draft would be made. When not auto tracing two sheets would be sufficient, one containing the line and point detail, the other sheet containing the screen areas.

When using auto tracing software it is advantagous to draw the line and point detail for each colour on a separate sheets (since the tracing software does not distinguish different colours) and the screen areas on another sheet. To maximize the efficiency of the auto tracing software try to:

minimize intersecting lines - this is largely acheived by using separate sheets for different colours but there are other opportunities to reduce them such as not drawing the tags on fences.
avoid dashed and dotted lines - draw each dashed and dotted line as a continuous line and identify each with a label ensuring this does not butt the line (intersecting line!). For distinct corners put a dot so this information is not lost when enhancing the traced lines.
draw only outlines - do not fill solid objects such as buildings and only draw vegetation edges, again labelling them.

Remember to register each sheet with sufficient marks, be especially careful when scanning the drafts in part.

Survey draft for digitising or pen and ink

A survey draft to be used for digitising or pen and ink drawing can be drawn on a single sheet using colour to differentiate between the classifications of lines and areas. The map is either digitized or traced directly from the survey draft. The computer output can be produced at final scale while pen and ink drawings are photographically reduced to map scale prior to printing.

Is a survey draft required?

When drawing a map using a computer is it really necessary to produce a survey draft first or can it be drawn directly from the survey sheets? Both methods have advantages and disadvantages , the most important of which are described below:

Preparing a survey draft

Discrepancies in fieldwork can be resolved before cartography
When working away from base without a computer
When more than one person working on the survey?
When autotracing results are more likely to be successful
Two occasions where errors can be introduced
It is time consuming

Direct from survey sheets

Cartography can proceed at the same time as the survey
No survey draft - saves time?
When scanning - fieldwork must be done on separate sheets ^*
When scanning - field work presentation must be of a high standard ^*
When scanning - dirt and erased lines may show on scanned image ^*

This may increase time in the field ^*