I’ve spoken to Ecologists (QGIS users) and Landscape architects (CAD users) and here’s how to improve collaboration and make Biodiversity Net Gain (BNG) Assessments quicker and easier.
Introduction
Over the years landscape architects and ecologists have been like 2 tribes. One using CAD to design, the other using (Q)GIS for site management and spatial analysis. With Biodiversity Net Gain (BNG) there is a real need to collaborate. On a technical level, this means integrating CAD designs to QGIS to create the ‘post-development’ GIS layer. However, as we shall see, there are opportunities for a deeper, more collaborative, approach to habitat design.
At this point, I should confess I’m not a CAD user, or a practicing ecologist, or a landscape architect. I’m a GIS specialist. And I love to collaborate, working daily alongside both ecologists and landscape architects. I wanted to better understand the issues both groups experience around QGIS-CAD-BNG so I reached out and spoke to both groups.
By the end of the article, you will:
Have a better understanding of a landscape architects’ role in BNG.
Have an appreciation of some of the common issues QGIS users have when integrating CAD data to QGIS.
Be able to understand what is causing the issues from a CAD perspective.
Better communicate, and collaborate, with landscape professionals / CAD users.
The role of Landscape Architects in BNG Assessments
Whilst BNG is, by its nature, ecological, the role of landscape architects is often fundamental. While an ecological survey will establish the current biodiversity baseline on a site, it will often be a landscape architects’ design that will define the biodiversity value post-development. A 2022 Landscape Institute policy briefing suggested that, for Landscape architects, BNG would mean:
liaising closely with project ecologists from inception
translating ecologists’ recommendations into plans, and
designing sensitively to retain key existing habitats.
The briefing also specifically recognised the role of GIS in delivering BNG assessments; for facilitating consideration of the project site in context, combining data sources, and enabling precise habitat area calculations. It also recognised that the “accurate translation of habitat boundaries between GIS and CAD is vital to avoid frustration and delays”.
Typical issues Ecologists face liaising with landscape professionals about BNG
So, what, specifically, are the issues QGIS users face integrating CAD data for BNG? To find out I asked the ‘QGIS for Ecologists’ Facebook group what would be their top priority for improving interactions with Landscape architects when delivering BNG? (thanks everyone that responded). Here are some of the responses, anonymised, and divided into 2 categories:
Data quality
“Send us geo-referenced CAD or even better, shapefiles with no gaps and overlaps.”
“Use polygons and lines properly! Instead of lines that self-intersect to represent polygons.”
“Use correct origin coordinates and at metre scale not mm.”
“We really don't need toilet siting, windows and 120 other layers with impenetrable naming protocols.”
Habitat classification
“Improve pallets - bring them in line with UK habitat names - what's wildflower planting?”
“Discussing how the habitats will be translated into BNG categories.”
“Learn to create localised habitat - why plant Scottish bent in Yorkshire?”
It seems the process of integrating CAD data for BNG is really 2-fold:
Correcting any issues with the geometry / spatial data and
Translating attributes to UK hab.
But where do the issues with CAD data originate, I asked myself?
How data issues arise in CAD and how they can be avoided
To understand where the above issues are coming from I needed to speak with CAD users. So, I reached out to some friendly landscape contacts (thanks especially to Suzanne Hyde, & Marketa Hermova). It became immediately clear that there is a much wider range of CAD systems compared to GIS, and that they don’t all work the same way. However, in general:
Most CAD systems don’t support map projections, so co-ordinates are vital for ensuring data is geo-referenced. If they have been changed (e.g. from meters to millimetres) this will invalidate the projection when the data is brought into QGIS.
Often the CAD file used for a landscape design originates from an architect, who in turn begins their work by importing a Topo survey or Ordnance Survey (OS) data layer. If the data is subsequently moved and rescaled from an arbitrary point (e.g. so the architect can view the site ‘front on’) it can be impossible to return to the original (correct) location. Also, because of all the different people that have worked on it, a CAD file can contain lots of different layers of information. These can be removed before providing to the ecologist, but often aren’t, making it harder to interpret and work with.
In CAD, different types of features are drawn as different layers. The various layer names are then converted to attributes in a table when imported to QGIS. Poor layer management in CAD can thus result in data can be added to the ‘wrong’ layer. For instance, if a woodland is drawn on a building layer, when this is brought into QGIS it will be incorrectly classified as a building.
Enclosed shapes (e.g. habitat areas), which in GIS are drawn as polygons, are frequently drawn in CAD using lines which don’t ‘close’ to make ‘contained’ shapes. Using polylines, and properly closing them, would solve this.
Data in a CAD files can either be in the ‘model space’ (map data) or paper space (page design). If a CAD file is provided to an ecologist containing both, it can result in non-spatial (page) data being added to the map in QGIS. In addition, other elements can appear at random locations on the map in QGIS. For instance, if the CAD operator leaves:
the map key in the model space so that the pattern scales with the page design
design revisions at different locations in the model space and doesn’t remove them.
Improving collaboration between ecologists and landscape architects
The translation of habitat boundaries between GIS and CAD is vital to the accuracy of a BNG assessment, and to avoid frustration and delays. Yet, as we have seen, every time data is moved between CAD and QGIS there is potential for errors. So, given what we now know about the issues ecologists see, and how data is created in CAD, what lessons can be learnt? Here are a few thoughts:
Landscape architects should:
Be aware that the main map projection used in the UK for BNG assessments is ‘EPSG 27700: British National Grid’ (the original BNG!), where Eastings and Northings co-ordinates are in hundreds of thousands of metres (100,000s). While is it OK to work in mm the co-ordinates must be set to m before providing data to an ecologist / QGIS user, otherwise the data will be in completely the wrong place and will need to be re-scaled and positioned.
Page elements, legends, unnecessary layers, and design revisions, should be removed before sending the file to an ecologist, which will make it much easier for them to interpret.
Ensure good drawing practice (e.g. using closed polylines for enclosed shapes) and good layer management to ensure data integrity and reduce the amount of data manipulation required.
Ecologists should:
Discuss their needs with landscape architects, explain what is necessary for a BNG assessment and ask for unnecessary layers to be turned off before export from CAD. BNG is new for everyone, and landscape architects are not used to their designs being used for this purpose.
Be specific about projection needed, how co-ordinates should be set to meters, and that habitat area calculations require polygons, which will have to be created from lines if the CAD operator hasn’t used closed lines.
Request data in ASCII format DXF, which will make it easier to import and work with the data in QGIS.
Discuss the UK Habitat classification with landscape architects and whether plant codes & pallets be more standardised to aid interpretation.
Conclusion
I hope you have found the article useful. I certainly feel like I have learnt through researching and writing it. And I think that really is the point. BNG is new for everyone and its incumbent on all of us to learn. With a few small adjustments, improved communication, and simply having a little more consideration when providing or requesting data, I’m sure integrating CAD data into QGIS for BNG assessments will get a lot easier. Who knows, maybe in time we’ll see a deeper collaboration become standard practice, from landscape architects doing the design and handing it over to the ecologist for assessment, to a more iterative approach where ecologists co-design the habitats with the architects.
Maplango have deep experience working with Ecologists and Landscape architects and offer a range of training and support options, meaning you spend less time wrangling CAD data, or trawling YouTube for the answer. Get in touch to explore the approach that’s right for you. With our video courses, live courses, email & what’s app support, and consultancy services, we’ve got you covered. Book a free, no obligation, chat using the calendar below, or get in touch by email or phone.