Deviants

[MattS]

Firstly, from what I can see in old mapsheets, all 'old topographic or topographic survey' sheets (from Svy Corps, Natmap, Sunmap or NSW Gov) were laid out on lon-lat edges, so they were TN up. Of course some government mapping (like Forestry and National Parks Departments) used a different rotation entirely, and it varied a lot between maps, but this was usually fairly obvious from the grids (if present) and the compass roses (which on my maps were always present). But maps in the Topo series were always TN up.Then it seems that things changed with QTopo. Now the Topo geopdf mapsheets do not seem to be laid out on lon-lat edges. They do not seem to be TN up. Rather, as Tom B pointed out, they appear to be GN up. But NSW still uses TN up. If that is correct, can you say when and why the States diverged in this matter (without warning that I can see on the mapsheets)?

From personal experience, it's easier to auto-generate maps aligned with your (grid) projection. For example, I did try to generate a UTM map aligned to TN out of QGIS, and couldn't get it to work. Whereas it's pretty straightforward producing maps aligned to the relevant UTM grid.

Tom has pretty much nailed it.

It's not widely known that after the 2011 floods, we had to reprioritise a lot of mapping. As a result, our topographic mapping unit, which wasn't large in the first place, was wound down. That's because each 1:25000 map we produced was a labour of love and could take 3-4 weeks to create. And that's not counting the aerial photo, surveying and photogrammetry (which I used to do) that proceeded it. All this for a product which used to cost around $10 to buy over the counter. When you think about it, it's a wonder it lasted as long as it did. But we're in a verydifferent public service now. We boast maybe 1/4 the numbers we had 15 years ago. And I can't say too much about budgets, so I won't! So we had to think smarter about how to do things like bringing back topo mapping - the cost, however, is things will never be like they were 20 years ago. However, I am proud to say that we've gone from maps over 8% of the state to 100%.

When we create topo maps these days, we're generating them in whopping great bundles at a time with a topo map service as the map face (incidentally, this is why you'll noticed labels that overlap the map boundaries). We're basically creating them by UTM Zone which is why the edges are aligned to the grid. So it depends on the map projection used - if you use something like Web Mercator, GN and TN are the same.

I can't speak to the way NSW create their maps - we do have contact with them, but we don't usually get into the nitty gritty (although perhaps we should more often). But there's no rigid national standard for producing them. If they align to TN then perhaps they're using an Albers Equal Area projection or something similar.

As I may have mentioned in one of our official help desk responses, my options for customising the North Rose is pretty limited. I can do a custom version where I can choose the length of the arrows, but I can't change the line thickness and they end up thicker than I'd like and when the distinction between the True North and Grid North is so fine, it's all a bit counter-productive. I will be looking to add some G-M angle text to make things a little clearer and more useful.

Lastly, we will be updating our look and feel of QTopo in the next release. Not to bore everyone, but we've reached a point where resourcing and industry trends have pushed us in a certain direction. It shouldn't look too different though, maybe a little cleaner and more detailed (e.g 5m contours where available @ 1:25000 scale). When I have it more nailed down, I'll post more about it in the QTopo thread on the Qld sub-forum.

[tom_brennan]

I can't speak to the way NSW create their maps - we do have contact with them, but we don't usually get into the nitty gritty (although perhaps we should more often). But there's no rigid national standard for producing them. If they align to TN then perhaps they're using an Albers Equal Area projection or something similar.

The NSW and Geoscience Australia maps are all aligned to TN in the centre, but do use UTM projection (not Albers) for the relevant zone. The extents are always round half, quarter or eighth degrees - which is pretty handy because you only need the map code to know what the extents are. Eg 4066-4 Princess May tells you that it's a 1:50k map with N/S -15°30' to -15°45' and E/W 125°30' to 125°45'.

It looks like QTopo actually uses the same extent codes for the maps, but because the grids are aligned to grid north, the map area is the bounding box (possibly plus a bit of extra padding?) for the relevant extent ie a QTopo map will be a bit bigger than a GA or NSW SS map would be at the same latitude, and there will be some overlap with surrounding maps.

For those who are interested, the 4 digit codes (eg 9131 Gosford) are for the 1:100k maps (0.5° x 0.5°). Codes with a single suffix - which can be a letter (N/S) or a number (1/2/3/4) are 1:50k maps. N/S is used if they are half of the previous map sheet. Numbers are used when they are a quarter sheet, with the numbering going clockwise from the top right. Codes with two suffixes (eg -2N, -41) are 1:25k maps. Similar to the 1:50k maps, ones with a letter are half of the relevant 1:50k area, and ones with numbers are a quarter of the 50k map, with the numbering again going clockwise from the top right. The codes are all theoretical - not every possible code has a matching map!

The red lines in the diagram show the 1:100k map bounds. The green lines show 1:50k (theoretic) map bounds. The smallest boxes show the 1:25k map bounds.

2024-07-19 10_03_00-QGIS.png (22.41 KiB) Viewed 1133 times

QTopo's 1:10k maps look like they are 1/4 of the 1:25k map, and have an additional digit eg 8646-424.

For the more nerdery, the formula for the 1:100k map codes is Long x 2 - 211, Lat x 2 + 98, using the Lat/Lon from the bottom left, same as you do when reading UTM grid refs. Eg the bottom left corner of the Gosford 1:100k sheet is Lon 151°, Lat -33.5°, which gives 9131 as per the pic.