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Counties from the Air

A guide to using aerial photographic maps as an aid to biological recording and environmental studies

Dr David Corke – Lopinga Books Ltd

Copyright considerations

The aerial photographic maps on the CDs retailed by Lopinga Books Ltd are copyright by Getmapping plc and published by Bluesky International Ltd. This document is not authorised by either the publisher or copyright owner and should not be taken as a guide to what you may legally do with the imagery contained on “Counties from the Air” CDs. If you are in any doubt about what the purchase of one of these CDs permits you to do, you should contact the publishers (www.bluesky-world.com) for details.

The CDs are sold for private or educational use, so if you are planning to use the data as part of your work (for example, biological recording as part of your employment by a conservation body) you should seek permission from the publishers. Whoever you are, if you plan to publish an image derived from all or part of the data on the CD, you will need to buy a licence to do so: this can be done online at  www.getmapping.com  where the charges (based on the size of area covered and number of copies to be made) are fully explained.

You must not sell or give copies of the image to anyone else: they should buy their own CD in order to use the data legally.

The author & publisher (Lopinga Books Ltd) of this document give no assurance whatever that the processes described are permitted within the terms of your user licence. If you have any doubts, please check with Bluesky International Ltd.

What’s on the CD?

There are four files on each “Counties from the Air” CD:

Using ERViewer

The introductory “Getting started with this viewer” and the detailed “Help Topics” available on screen while you are using the program supply full details on all aspects of its use. This section is intended only to highlight a few features especially useful to those using the program as an aid to biological recording.

The things that you can do include:

Reading a grid-reference

When using the “hand” tool to move the aerial photograph around the screen, you cannot read grid-references. You need to select either of the two zoom tools or the measure tool. The measure tool is probably the most convenient: simply position the cross hairs (to the left of the ruler symbol) over the feature whose grid reference you need:

The first figure tells you how many metres the point is to the east of the “origin” of the Ordnance Survey national grid, the second the distance in metres north of the origin. The origin is a point in the Atlantic to the west and south of the Scilly Isles.

To convert this figure into a normal grid reference:

Take the first digit of the eastings and the first of the northings (in this example that’s 52) This is the number of the 100 km square in which the point is situated. Most maps today use a pair of letters instead of a pair of numbers to define the 100km square. Ordnance Survey maps show the numbers and corresponding letters for each 100km square they cover. Square 52 is “TL”

How many of the rest of the numbers you need depends on the scale at which you are working. For national or county level recording a grid reference of six figures is more than enough (it specifies a square 100 metres by 100 metres). So the six figure grid reference in this example is: TL658312. You might only be interested in which 10km square the point is in: in this example TL63

But if you are plotting the exact positions or rare plants in a wood for example, you may need a much more precise grid reference, maybe specifying which 10m sq the plant is in. In this example TL65853126

If you used all the figures: (TL65852783126536) you are locating the point to within one centimetre! It is absurd to do this using these county aerial photographs because, as you zoom in closer and closer, the image eventually breaks up into coloured squares with no visible details. These squares cover 2 metres by 2 metres on the ground and so that is the maximum level of accuracy you can possibly achieve with these images. [see More detailed images? If you need better resolution aerial photographs]

There is no way of directly copying the grid reference on the screen into a database on your computer. Using ERViewer all you can do is make a note of the reference and then type it in manually to your database. Using some other “GIS” programs you can automate this process and click a point on the photographic maps to enter the grid reference into a database files. See “Map Maker”.

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Saving part of the aerial photographic image

ERViewer lets you save a copy of whatever part of the county you have displayed on the screen and gives a choice of which format is used to store the image. This is very important as the “ecw” file format is only for specialist mapping programs such as ERViewer. If you want to incorporate the image into a word-processed document, modify or annotate it like a digital photograph or use it with a GIS program you will need an appropriate format. The size of the file you save will depend on three things:

Which format to choose?

Use JPG if the image is just going in a word-processed document. BMP or TIFF if you need to modify (and digitally enhance) the image using PHOTOSHOP or a similar program.

If you are going to use the map extract in a GIS program, the program will need to know the scale of the image and the grid-reference of one corner of the image. Using the “GeoTIFF” format will do this automatically with most GIS programs

Updating ERViewer

Click ERMapper Home Page under the HELP section (or visit www.ERMapper.com ) and you will be taken to the website of the company that created ERViewer. You will be able to download (free) a more up-to-date version of ERViewer (currently version 7.1, your CD has version 7.0). You will also have the option of downloading a free trial version of a much more versatile map image processing program called ERMapper

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Using Aerial Photographic images with DMAP

DMAP is the most widely used biological mapping program in the UK: used to prepare the great majority of published dot-distribution maps in national or local wildlife atlases. The simplest maps created with DMAP consist of two “layers”: a boundary outline defined in a “BDY” file of grid-references and the dots representing each record of the species mapped (in a DIS file or direct from some biological recording databases. Full details of the program, sample outputs and a free demonstration version can be downloaded from www.dmap.co.uk

The map shows the known locations of garden nesting song thrushes in the distrct of Uttlesford, NW Essex. Created with DMAP, the background photograph copyright by getmapping.plc

Instead of (or in addition too) the boundary outline of the study area, DMAP can have an image as the bottom layer in a map. So, for example, you might have an aerial image of a nature reserve, a line indicating the boundaries of different habitat types and dots representing the known colonies of a particular species. DMAP requires its image files to be in BMP format so it is easy to output these using ERViewer. The scale and grid-reference of the aerial image is not recorded in the BMP file so you should make a note of the grid references of the NE (top right of screen) and SW (bottom left) corners of the image while using ERViewer. Then save the BMP file and, in DMAP, use the OPTIONS – Map parameters screen to tell DMAP these co-ordinates. Then DMAP will be able to plot your species records directly on to the photographic image.

Full GIS programs

The “industry standard” GIS (geographical information system) programs are the American:

These are both massively expensive programs (although free trial versions are available). You can use photographic map images saved from ERViewer in these programs but if you can afford to own these programs you can afford to buy the detailed manuals and/or training courses that you will need to use them.

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Map Maker

Ordinary mortals who are spending their own money should try Map Maker, a British program which exists in a completely free form (Map Maker Gratis) as well as a more powerful and reasonably priced Map Maker PRO version. You can download a trial version of Map Maker PRO and use it for a month. After that, (if you don’t pay up) it automatically turns into Map Maker Gratis and you can go on using it. Also available for free download is a very detailed and excellent manual that is a good introduction to GIS in general as well as a detailed handbook on getting the best from the program. Anyone interested in GIS work of this type should test Map Maker: www.mapmaker.com

The map shows the footpaths, bridleways and green lanes in and around the parish of Wimbish, NW Essex,. Created with Map Maker Gratis, the background photograph copyright by getmapping.plc

Map Maker can work with GeoTIFF files so it automatically knows the scale and position of your extracted aerial image if you save it in this format from ERViewer. Map Maker Pro can also use ECW files directly (but Map Maker Gratis does not have that option)

With an aerial photographic map on the Map Maker screen, you can easily create a database of records just by mouse clicking the position of each record. You can also measure the exact areas of habitat features that you outline (individual woods or ponds for example)

GPS & SAT NAV

The extent to which you can use “Counties from the Air” images in conjunction with Global Positioning and Satellite Navigation systems will depend on the specification of your GPS or SAT NAV equipment. Check what file formats (if any) can be imported and displayed by your equipment and then check whether you can create a suitable image format using ERViewer.

There is generally no point in trying to use aerial “bit-mapped” photographs with SAT NAV equipment: you need the sort of vector-mapped data that comes with the equipment: so that the program knows the names and positions of each road and can draw maps quickly at any scale required.

For biological and environmental recording purposes (and for walking visits to the countryside) a workable system is to use a standard, hand-held GPS unit linked to a portable computer running Map Maker PRO. You can have Map Maker display an aerial photograph of where you are  and superimpose your position from the GPS link. This also enables the positions of individual observations to be recorded or outlines created by (for example) walking around the edge of a field and recording the grid reference at every point where you change direction. For most GPS work you do not really need to display the aerial photograph but doing so enables you to check the accuracy of your GPS waymarks. GPS is not 100% accurate and it can be useful to compare the grid reference reported by the GPS with that of your location identified on the aerial photographic map image (which matches OS maps exactly).

If you wish to map a boundary (of a wood for example) it is almost always better to do this at home using Map Maker and the aerial photograph than to record waymarks as you walk round the actual wood. This is because you get more accurate grid references from the aerial photograph than the (at best) 5 metre accuracy you get from GPS.

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More detailed images?

Each “pixel” (dot in the photograph) of a county aerial photograph covers 2 metres square. This is good enough to see every tree, hedge, small pond etc in the county and for most purposes is all you will ever need. If you need to “zoom-in” really close, because you are interested in the details of a small area (a big garden, a smalll nature reserve etc) you can use the CD to identify the exact area you are interested in. When you have noted the grid references of the area you want, go online (www.getmapping.com) and order a high-resolution image of the area. The highest resolution available is one pixel covering 25 cm square: i.e. 64 times more detail than on the CD of the whole county. When you buy you can select the type of licence you need: simply the right to make one or two copies or pay more to permit you to include the image in a published book or leaflet.