Bushwalk Australia

Does anyone know for sure what the small blue triangles represent in the 2017 series NSW topo maps?

This is not shown in the map legend, and the features have disappeared from the 2022 series topos.
In some very old maps this kind of symbol was used for a small dam.

Looking at layers in the geopdfs the symbol seems to be 'ancillary hydro point' which can mean lots of things (thus it means nothing).

I was going to use them as more reliable water points on a long hike, but now I think that would be a mistake.

If all else fails, I guess I will go and look at a few (carrying lots of water)

Do you have an approximate grid reference for where one is located?

Sure, the left one above is at
56J 537208 6839064.
They are all over the place on watercourses away from inhabited lands.

According to the NSW Water Theme Feature Server
https://portal.spatial.nsw.gov.au/serve ... tureServer

It represents a stream dissipation point
I am not sure what to make of that but seems to be the location where a stream loses its defined channel and disperses or disappears into the surrounding environment.
[Edit]: The layer; AncillaryHydroPoint, also has a feature described as a "sink", so I am thinking it is more about dispersing into the general area rather then disappearing like it might do in a karst area.

Probably not the place to think you may pick up water.

I walked part of the Northern Rivers Rail Trail this morning, and went past some of those triangles. As best I can recall, at two of them were concrete works presumably to stop bank erosion. At a third I don't recall seeing anything in particular. They definitely weren't dams. If I walk it again, I'll take a bit more notice.

Thanks guys. According to database notes it can be lots of things, including a 'contracted node', whatever that means in context of watercourse mapping. I think the take home message is 'Don't rely on finding water here'.

Interesting question!

I hadn't ever really noticed those points before. I mostly look at maps in the Blue Mountains and I don't think it's used much there.

I had a look back at the Series 1 maps. It reminds me of why it's handy to have those old maps!

So, it looks like they indicate points where the watercourse stops being a defined watercourse, such as when it runs into a cliff or steep areas.
I'm not sure exactly how they would have mapped them, possibly just guesses based on the topography as they wouldn't have been surveyed from the ground.

So in the series 1 maps, they had them showing the ends of watercourses, with no watercourse line after that.
Then on the later series, they continued the watercourse but still showed the 'dissipation point'.
And then on the most recent ones you just have the full 'watercourse' but the point is still in the data, just not displayed on the map?

These are the minor things which get lost along the way when you go from maps produced and individually reviewed by cartographers, as opposed to "auto generated" based on rules.

Thanks Allchin09. Yes, it is sometimes that, but sometimes not. The triangle apex in my area usually points roughly E. This can be upstream, downstream or across the stream. They can be on perennial streams in areas where the stream obviously continues.

I now understand that an ancillary hydro point can be lots of things (so the decision not to show them in 2022 makes sense to me, as I can not always guess which applies to a particular point).

Here is a short list:
1: Bore
2: Lock
3: Rapids
4: Spring
5: Tidal Limit Marker
6: Waterfall
7: Dissipation Point
8: Contracted Node
9: Hydro Data Management
10: Regulator
11: Barrier
12: River Gauge
13: Sink

or:
NSW Ancillary Hydro Point data represents a location that has unique hydrology characteristics or monitors or controls stream flow or manages hydrographical spatial data integrity...

Anyone who is interested can follow up in https://www.spatial.nsw.gov.au/__data/assets/pdf_file/0005/195449/DTDB_feature_reference_guide_27042015.pdf,
or https://data.nsw.gov.au/data/dataset/3dd8def0-ce05-4532-8a91-b63cc2edd20f/resource/76237880-f5e1-4857-b621-a717d2d600f8/download/datasetproducttitle_nsw-ancillary-hydro-point.pdf

I'm not sure I follow.

Your second screenshot example shows the same sort of features on the series 1 topo as it did in your first example.

Series 1


Interestingly, the 2011 edition appears to be similar, just showing the creeks where they 'exist' in the same way that the Series 1 does, but doesn't show little triangles at the ends like the S1 does.


Then 2014, 2015 and 2016 are all similar to the current day maps, with lines being drawn along the whole watercourse. There are no little triangles though shown.


It's only the 2017 where those triangles appear on the map. Really, it should be a combination of the 2011 style (don't show the watercourse where it doesn't exist) and 2017 (show a little marker at the start / end of the watercourse). But that's not what's happened obviously.

Regarding the "ancillary hydro point" feature, the underlying data does differentiate between the various (13) types. This is stored as a domain value number which you can then use that pdf spec to work out what the number means, eg 7 = Dissipation Point and 6 = Waterfall.

Each type can (and usually is) styled differently on the topos. See below examples for what the data looks like in the topo database and on the 2017+ series topo maps

Thanks again Allchin09,

I think the NSW 2017 topo series maps I am looking at on Oruxmaps were delivered from the WMTS server. In that previous image you can see a blue triangle across a perennial section of Rocky Ck. Not in steep terrain.

It looks like you are getting extra information from QGIS, as domain values are not shown in Oruxmaps or Adobe Reader, and all 'Ancillary Hydro Points' that I have seen there look the same.

Just to extend your interesting series, the 2022 geopdf goes back to the '2011' handling, in that uncertain parts of non-perennial watercourses (and 'Ancillary Hydro Points' ) are again not shown (example below), This makes some sense to me, at least in dry weather, though in some cases it seems clear enough from contours where the water must flow in the wet.

Off-track wrote:The triangle apex in my area usually points roughly E. This can be upstream, downstream or across the stream. They can be on perennial streams in areas where the stream obviously continues.

I assume the fact that they all point E is just a styling stuff up.

There are other instances where SS have stuffed up the direction of point objects on the maps. For example, in their most recent maps, the waterfalls all point N-S!

Yes, the extra data is only when you retrieve the feature information, not the rendered tiles.

@Tom, did they also decide to change the order of those two waterfalls whilst they were at it?!

The funniest bit however about the waterfall symbols is that the dataset actually has a field for 'symbol rotation' ! Unfortunately it seems to just be 0 for many waterfalls (which is fine if you're drawing them as circles but not if they are lines) but not all. You can see in my screenshots above that a waterfall as a symbolrotation value of -5. I have seen Dissipation Points with non 0 values as well (but they don't seem to use that in the styling).

Off-track wrote:It looks like you are getting extra information from QGIS, as domain values are not shown in Oruxmaps or Adobe Reader, and all 'Ancillary Hydro Points' that I have seen there look the same.

As you listed earlier there are 13 different feature types in Ancillary Hydro Point. All those different features are rendered with different symbols.
1: Bore 2: Lock 3: Rapids 4: Spring 5: Tidal Limit Marker 6: Waterfall 7: Dissipation Point 8: Contracted Node 9: Hydro Data Management 10: Regulator 11: Barrier 12: River Gauge 13: Sink

Case in point in the area you were looking at there is an area with both a Waterfall and some Dissipation Points. Using Acrobat layers to turn off the Ancillary Hydro Point layer you can see that both waterfalls and dissipation points disappear when you turn off the layer



If you want to find out what other features are around, go to the feature server I mentioned in my first post scroll to the bottom and select the query page and put
ancillaryhydrotype=7
In the "Where" field. The number is the code for the type. Better you also select the option to "Return Count Only: True" or you will get a ton of data back.

From that I can tell you there are 7 Locks and 4019 Dissipation Points. Lots of the other types also so 'Ancillary Hydro Points' are not all the same on the PDF or the raster Topo's

Thanks again guys. I am learning a lot. I think these 'Ancillary Hydro Points' could be very useful in trip planning, if only their meanings were understood.
Sounds like they may actually be distinguishable by symbol in the geopdfs or wmts tiles, without each hiker having to learn Qgis.
User defined (=custom) waypoint symbols do not rotate in Garmin or Oruxmaps as far as I know. Cartographers (even AI ones) can do better, but we can usually get by without rotation if only we know what each symbol means.
What a shame they are not in the map legends (and missing from recent topo series). But maybe someone can help here with symbol meanings at least, to benefit all forum users.

As you listed earlier there are 13 different feature types in Ancillary Hydro Point. All those different features are rendered with different symbols.
1: Bore 2: Lock 3: Rapids 4: Spring 5: Tidal Limit Marker 6: Waterfall 7: Dissipation Point 8: Contracted Node 9: Hydro Data Management 10: Regulator 11: Barrier 12: River Gauge 13: Sink

johnf, can you give the symbol for each type? I could not figure it out from the link you gave.

Why would there be a "dissipation point" across a perennial stream (as shown above for Rocky Ck)?

It's a bit of work to find the right place and then post the picture of all the symbols.
If you go to Alex's map site, use the location search and then type in Bore or Lock or Rapids or Spring or Waterfall you will find a location with that in the name and then navigate to it and look at what symbol is there, You might have to select a different baselayer.
There are no current 8: Contracted Node 9: Hydro Data Management 13: Sink in NSW
There seems to be only 1 Barrier at Woronora Weir
The others seem to be just labels, no symbols.

Allchin09 wrote:@Tom, did they also decide to change the order of those two waterfalls whilst they were at it?!

Oh dear, I hadn't even noticed!

I suspect that it's probably a labeling/styling issue again. The label for "Silver Cascades" is on the top right of the feature, and the label for "Victoria Falls" is on the bottom left. So they just look incorrect! Not uncommon with automated labelling.

Interestingly GNB doesn't even have Silver Cascades ...

Thanks johnf. I tried what you suggested. Alas, these 'Ancillary Hydro Points' on the 2017 NSW topos are far less useful than I hoped.
eg: only 3 rapids in NSW (and no symbols for them)???
Some symbols (waterfalls at least) are in the map legends, but only some (large) falls are shown.

I think these are the best maps available, but they have many errors and inconsistencies.
A good reminder not to expect too much from these maps or the NSW SS.

tom_brennan wrote:I suspect that it's probably a labeling/styling issue again. The label for "Silver Cascades" is on the top right of the feature, and the label for "Victoria Falls" is on the bottom left. So they just look incorrect! Not uncommon with automated labelling.

Yes, I think you're right.

The new 'topographic' basemap which shares similar styling appears correct