WAMS Maps - Colin Cook - October Tramper
The WAMS (Walking Access Mapping System) website was very briefly reviewed in a recent issue of Wilderness (August 2020, p. 12). Although describing the website as ‘the complete trip planner’ and ‘unbeatable’ as a ‘comprehensive map of New Zealand tracks and public land’ the reviewer also found the site ‘difficult to use and glitchy’.
Here then is a step-by-step guide to accessing and using the site. (An instruction to select or deselect an item means ‘left click’ on the item).
Accessing WAMS maps
- Go to https://maps.walkingaccess.govt.nz/OurMaps/
- Select Outdoor Access Map, the top left of several map versions which are offered on the screen). Note there is also a link on this page to an extensive help section.
- Wait for the map of New Zealand and the Layer List panel to appear. Centre the image by left click and drag.
- In the Layer List panel on the right deselect 'Public Access Areas' and ‘Property Information’. Then close the panel (select X at top right corner).
- The black band at the top of the screen (hereafter called the Menu) lists a series of ‘widgets’. Select Basemap to open the Basemap Gallery panel. (If ‘Basemap’ is not showing, select ‘More’ from the Menu and then select 'Basemap').
- In the gallery select NZ Topographic Basemap. Then close the panel (select X at top right corner).
- Select the ‘+’ icon (top left of screen) to zoom into the area of interest (Select any point on the screen and drag to keep the map centred as required.) It takes maybe eight or nine clicks before the switch to Topo50 occurs.
- To switch to aerial photography, select the Basemap widget from the menu and then select NZ Imagery Basemap. Close the panel and zoom in or out as required. Note you can zoom in further on Aerial Imagery than on Topo50.
There is a search bar top left of the screen. (Execution of a search may end in a high-zoom screen. Zoom out to recover the Topo50 map).
- From the menu select Add Data.
- From the ‘Add Data’ panel select File (top right hand corner) then select Browse. This takes you to your computer or cell phone file listings which you must move through to locate the gpx file you wish to display.
- Select the file and then select Open. The trace is now displayed on your WAMS map. You can view the trace on aerial photography by selecting ‘NZ Imagery Basemap’ from ‘Basemap’.
Your file now appears in the ‘Layers’ panel and can be deselected if desired.
- Follow the method described earlier to access the section of topo map or aerial imagery you are interested in.
- Select Draw / Measure from the Menu (or under 'More'). A ‘Draw/Measure’ panel appears on the right of the screen.
- From the first line of icons at the top of the panel select the wavy line (this allows you to draw lines with curves and corners).
- The panel now extends further down the screen. Against Style you may choose ‘Solid’ or ‘Dash’ etc (just click in the box to see the options). The various options are also offered visually. You can also adjust the Width of the line.
- Selecting a colour is trickier: select the Colour box and move the vertical slide. You can also go into the colour square to further adjust the colour.
- Move the cursor onto the map. An instruction appears saying 'Press down to start and let go to finish'. Draw your line. (Notice if you deselect the wavy line icon you can adjust the map as required. Reselect it to start drawing again).
- Right clicking on your line allows you to delete, edit etc.
- Using screensave or some other method you may now capture as an image file the piece of topomap or aerial imagery showing the drawing.
Once you have a drawing you can export it as a gpx or kmz file. (Export as gpx to display on topo map, export as kmz to display on GoogleEarth.)
- On the Draw/Measure panel close Appearance and open Drawings.
- Click on Select All.
- Click on the box GeoJSC and select GPX or KMZ.
- Click on Export. The file is sent to your computer's Download folder with file name export.gpx or export.kmz.
Many GPS navigation programmes automatically report trip distance and/or display an elevation profile. Once you have exported a gpx or kmz file you can use other programmes to display a trace and to calculate distance and total climb. (Note exported files are routes, not tracks).
Help is also available at contact [snail] walkingaccess [period] govt,nz. I have found the response to emailed questions to be both prompt and pertinent
WAMS Maps - Colin Cook - November Tramper
Using WAMS to find trip distance and total climb
This article concludes the discussion of the WAMS website begun last month and adds some comments on estimating trip parameters such as distance and total climb.
If your trip had an off-track component, perhaps the primary reason for importing the gpx file into WAMS is to see where you actually went! But once it’s there you can see the elevation profile and measure distance and (indirectly) total climb.
- Import your file as outlined above
- From the Menu open the Elevation widget. Left click on Select line and select the track (it turns fluorescent green when selected). After a short time, an elevation profile, height versus distance, appears in the lower half of the screen.
- Placing the cursor on the profile shows the elevation at that point and also the net altitude above (green) or below (red) the track start point. Total climb can be estimated in greater or lesser detail by reading off the elevation of local high and low points along the curve. (See the discussion below regarding total climb estimates.) A red cross also appears on the base map to indicate the corresponding point on the track.
Alternatively, you can proceed without importing any file. (In other words, you can find the elevation profile for any line you like to draw on the basemap.) First get the appropriate basemap (topographic or NZ Imagery etc) up on the screen. Then:
- Open the Elevation tool. A panel appears across the bottom of the screen.
- Click on Measure then Draw Line at the top left of panel. (To reveal more of your topo map click on the double arrow head top right of the panel which will then minimise at the base of the screen).
- Click at the start point of your route then at points along the route to define the total route.
- To end the process, double left click.
- Maximise the Elevation panel by clicking on the double arrow head. After a while an elevation profile of the route will appear.
Critique of distance and total climb calculations
A single GPS measurement (a ‘data point’) comprises four numbers: latitude and longitude (which determine position), elevation and time. Measurements are made every few seconds and a gpx file covering a tramping trip will contain thousands of data points. This data can then be used to calculate total distance travelled and total climb. It is the nature of measurement that no measured value is perfectly accurate, (in general time will be most accurate, elevation least accurate), and this affects calculations.
1. Track length or total distance travelled
The track programme calculates the distance between successive positions and adds all these distances to get the track length. Suppose you are walking a horizontal straight line. Measured positions are likely to fall on either side of the line. Joined-up positions will therefore zig zag and so overestimate the distance walked. On the other hand, when you change direction, the joined-up positions will tend to cut the corner and so underestimate the distance walked. Together, these two effects will tend to cancel each other, so maybe calculations of distance travelled are not too bad.
2. Total Climb
No such happy cancellation occurs with calculations of total climb. Suppose you are sidling at constant altitude along a hillside (‘contouring’). Measured elevations will fall both above and below the line of travel. Obviously points above the line lead to an overestimate of the total climb but so too do points below the line, since the data points will tend to return to the line of travel, thereby recording a climb. Similar arguments apply even if not contouring. For this reason, estimates of total climb are always an overestimate, quite often by a considerable amount.
Improving calculation accuracy
Programmes that calculate distance travelled and total climb no doubt have various ways to try and correct for these sorts of errors. For example GPS Track Editor2(approve sites) can be set to discard dubious points based on speed: if the computed speed (=distance/time) between two adjacent positions is say 36 km/hr (=10 seconds per 100 m) and you’re not Usain Bolt then the measurements are probably inaccurate. Data points are then discarded until a reasonable speed results.
Correcting for over-estimate of total climb is more difficult. I have tried averaging data points: each successive set of say three elevations is averaged (that is average elevations 1, 2, 3 then elevations 2, 3, 4, then 3, 4, 5 and so on) and then total climb is calculated from the average elevations. This invariably reduces the total climb value, by more if the average is over five points or seven points and so on, but where one should end is anyone’s guess.
There are ways to check values calculated from gpx or kmz files. For example, estimate the total climb by looking at topo map contours; this will lead to an underestimate since bumps of less than 20 m height gain will not show up. (It may be that some programmes effectively do this.)
Also, drawing a line in WAMS in ways outlined above will ignore the many twists and turns and ups and downs of an actual track. In this way you get a lower or under-estimate to go with the (probable) overestimates from the gpx file of your trip.
1 The question of errors or uncertainty in calculations of total climb or total height gain is much more thoroughly canvassed in The ups and downs of total height gain by Reid Basher, the Tramper, Vol. 89, No. 6, pp. 4-6.
2 Thanks to Andrew Nicholson for informing me of this programme which can be downloaded free off the Internet. [Colin Cook adds: ‘Since preparing these two pieces for the Tramper there have been continuing minor evolutions of the WAMS website. Any consequential tweaking of instructions/descriptions should be well within readers' capabilities’].