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Celtica Mapping 2011 - 2022

How we map a school or park site

There are five stages to producing the finished map.  We do not normally survey the site from scratch as defining the boundaries and fixing the buildings is a time consuming and therefore expensive option.  Instead we begin by using a 1:2,500 Ordnance Survey map of the site. Unlike the familiar Landranger or Explorer maps this is a black and white outline map usually used by planners.  There are no contours, and there is no indication on this whether lines represent walls, fences, hedges, ditches or just changes in surface, for example between the playground and field. Neither is there any indication of what is grass, tarmac, paving, woodland, or undergrowth, and the finer detail such as individual trees, bushes, play equipment, bird tables, willow arches or goalposts that we would normally include on a school map is not included.   Indeed, school sites are dynamic and may well have changed since the last O.S. map update.

1. Preparation  Our first stage is to draw a basemap from the O.S. map.  If you send us a paper map of the site we start by scanning it. We use this scan as an on-screen background which we trace over to obtain a digitised framework map of the site.  If we receive mapping data in digitised form (as a .dxf file) then we can import it directly, and we know the scale will be accurate.  This is therefore our preferred method of getting data.

At this stage we often cannot tell what the lines we have traced represent but this will become apparent when we actually visit the site.  We also decide upon the final scale of the map at this point. The eventual aim is to produce a map which will fit comfortably on to a single sheet of A4 paper.  Why A4?  Because this is the size of paper that schools can most easily reproduce either by colour photocopying or by printing from a computer. Typically, for a small primary school the chosen scale will be between 1:400 and 1:800, but may be 1:1,500 to 1:2,500 for a secondary school.  We always stick to round figures (the old inch to the mile maps were 1:63,360) as this provides a much easier basis for teaching the concept of scale. For example, at 1:600 one centimetre on the map will represent exactly 600cm. or 6m. on the ground.  We enlarge the basemap to the chosen scale, and print it out.

2. Surveying  This is the stage where we collect all the detail for the map. Using the basemap under a sheet of waterproof tracing film we survey the site in a sytematic manner. We check the scale of our basemap against a measured straight line (for example a boundary fence or playground edge) as all our subsequent conversions of ground to map distances will be wrong if this is not correct.  We usually start surveying with the buildings, looking for any changes since the O.S. map was produced. There are frequently extensions to add, and perhaps old buildings to remove. Often new fences have been added to meet the needs of the Foundation Phase, or disabled access ramps added by existing steps. We walk the site boundaries and note if these are fences, hedges or walls. We add all the detail that is semi-permanent - large single trees, willow features, climbing frames, fixed benches or picnic tables, recycling skips and so on. These are added by their position relative to identifiable points on the basemap, for example fence or building corners. On complicated sites having fixed secondary detail, for example the boundaries of school gardens or environmental areas, we then use these boundaries to fix the detail within. Exactly what detail we choose to mark depends upon the size and nature of the site. On a large site it may not be possible to mark individual trees without them becoming packed too close together, in which case we will use the “scattered trees” symbol, while on a smaller site mapped at a larger scale they could be shown individually.  

At a school with very few features for providing good control sites for orienteering we may mark fixed litter bins.  But at another school where there are plenty of suitable features we would leave the litter bins out. In some instances we have been reduced to marking drain covers, although these are normally omitted. Our aim is always to make the finished map attractive to look at, clear to read, without being over-crowded with minute detail, but with sufficient detail that varied orienteering courses can be planned. The surveying can take anything between an hour-and-a-half and a full day, depending on the size and complexity of the site, and how many changes have been made since the O.S. map which was provided as our basemap was last updated. Finally we check the direction of magnetic north with a compass.  

3. Drawing up  We scan the tracing film to create a bitmap file.  We now start a new map, with two background layers which we align – the scanned survey and the previously drawn basemap.  We now trace over the lines, but this time using the correct symbols for a wall, fence or hedge etc.   We fill the open areas with the correct colour - yellow for grass, green for dense vegetation or brown for tarmac or paving, and mark the point features with the correct symbols.  We try to do this soon after visiting the site relying also on memory to supplement the recorded detail.  Once finished we print out a draft copy of the map.

4. Checking   Unlike some mappers we feel that a re-visit to the school is important if we are to produce a high quality and accurate finished product. As checking the map takes considerably less time than the surveying visit we normally try and combine several checking visits in a day, thus sharing the cost of travel between several schools.  If this is impossible we may, in order to reduce the travel costs we charge, ask you to check the draft map.  If so take time to check it.  Circle errors and number them, then give details on a separate piece of paper.  If necessary draw a sketch, with distances indicated where appropriate, to show how an area should have been drawn. Once checking is done we can complete the map.

5. Finishing the map   Corrections are incorporated.  Orienteering maps are always aligned to magnetic north.  At present there is little variation between this and grid north (to which the O.S. basemap is aligned) but it will nevertheless make teaching map orientation using a compass, or teaching basic compass work easier if this magnetic variation is removed.  The map now has its border, title, scale bar, scale statements, north lines and the key added.  Finally, as it is based on an O.S. map the standard O.S. copyright statement and local authority (or other body) licence number must be put on. The map is then finished.  

All that remains is to print out a good quality paper copy, save it to a CD in three different formats (jpg,  OCAD9 and pdf), and package it, together with our 8 page advice booklet, for the school.  You will be unable to open the OCAD file immediately as you will not have an appropriate viewer on your computer, but we include it for two reasons.  You can download a free OCAD viewer from the OCAD site, or download the free Purple Pen course setting program, which also allows you to print OCAD files with or without overprinted courses.  Printing in this way gives the highest quality reproduction. In particular some colours in pdf files become a little altered.

Keep the OCAD (.ocd format) file safe as it will enable future updates to be made with a huge cost saving over only having a paper copy.

O.S. Map of the area.  The site to be mapped is extracted, shown here bounded in red


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