Island Maps: The Years after Meacham to World War II – Part 2 – Aerial Photos and Topographic Maps

In one of my earlier posts, I described how interest in seeing things from on high had its origins in ancient times and, with the invention of photography and the advent of the aeroplane took on an extremely important role in providing new data for mapping purposes and the study and analysis of the configuration of the land for agriculture, forestry, and mining, but also for extremely accurate recording of the progress of World War I.

It was when I flew, for the first time ever, from my new home in Montreal to the Island, that I became intensely interested in the view from the air and what it could tell me about the world I knew well from the ground. It was another of my epiphanies.

1958 – My world in Tignish. – Flight Line A16096-93, Crown Copyright.


1935 – The First Aerial Survey of the Island

Aerial photography would in time play a very important role in the survey and study – among various disciplines – of Prince Edward Island. In the years after the First World War there was a powerful push by the Canadian government to begin the exploration and eventual mapping of the western provinces of the country whose geography was largely unknown. There is a very fine description of this in Thomson’s Skyview Canada. After the war many air force fliers became bush pilots and played an extremely important role in opening up the western hinterland for industrial exploration. Soon the R.C.A.F. began to invest more and more money in the development of new aircraft, especially those capable of landing on water far away in the bush, and a very high degree of expertise in adding aerial photography to their activities was achieved. Their work was assessed and received the highest possible praise when in 1925 Col. H. St. J. L. Winterbotham, chairman of the air survey committee, British War Office, came to Canada to study the methods of topographical and aerial survey methods developed in the country. His praise was so effusive that I feel compelled to include a portion of it here.

He reported to the 38th meeting of the British Air Survey Committee and it is recorded that “the chairman took the view that in regard to mapping at small scales, the experience of Canada carries such weight that this Committee may rightly look to her for development of this branch of survey while this Committee proceeds with the investigation of more general methods. Moreover, the courtesy of Canadian officials, their anxiety to help and their keenness in the pursuit of required ends, together with the variety of purposes to which aircraft are applied, all place Canada in the favored position of leading the Empire in many branches of aerial work. The wealth of their experience in the particular branch of aerial survey will be generously placed at the disposal of other parts of the Empire, whenever the necessity for advice and technical assistance arises.” In his report to the Royal Geographical Society, Winterbotham added: “I should like to record . . . [the] exceptionally close and mutual understanding between airman and surveyor which exists in Canada as, I think, hardly anywhere else. Surveyors fly regularly in the ‘boats’ used in the lake districts and airmen concentrate on problems of navigation. There is everywhere the keenest interest in method and instrument and a marked absence of that sloppy over-confidence or wilful pessimism we have seen sometimes elsewhere in airman and surveyor respectively.” (Thomson p. 55).

Perhaps a note on the techniques employed by the Canadian aerial photographers would also be appropriate at this time.

Thomson p. 54

There were two kinds of photos taken in the process of aerial surveying. Oblique shots gave you a “top of the mountain” impression of the land below in three-dimension relief, low or high, depending on the angle of the camera. The lower your angle of observation the closer you came to the landscape view. The other technique, the vertical shot, gave you an exact outline that could be transcribed and rectified into an actual map.

Air Marshal C. R. Dunlap, a Cape Bretoner, left an account of the technique employed in carpet surveying of vast areas. What was most feared was a diversion in the flight line that would result in large areas being left out or photographed with insufficient overlap to connect one flight line to another and to permit the creation of a 3-D effect with a stereoscope.

“Photo survey in those early days,” Dunlap has stated, “called for precision flying of a high order. It was necessary to fly straight and level for 60 miles and then turn and do a parallel course in the reverse direction, a mile or so removed from the previous line of flight, and so on throughout the day. Overlapping vertical photos were taken as one progressed along the lines . . . Also, if all went well there was lateral photographic overlap in as much as distance between the lines took care of this, provided that one’s navigation was precise. It was a tough league as the man in charge was known as ‘no gap’ Jellison. Rivalry sprang up over which one of us could go the longest period without the appearance of a gap in our photography. Believe me, one’s shortcomings could not be concealed for long because the 500 or more photos per day were developed and back in our possession in less than a week, to be laid out on examining tables for detection of forward or lateral gaps.” (Thomson p. 64).

The vertical aerial photograph only showed you in outline form the lay of the land. However, if you placed two photos with overlapping sections of terrain side by side and looked at them with a very simple viewer called a stereoscope, everything would spring out in high relief, and you then got a very enhanced view of the terrain.


The 1935 Aerial Survey

Although nowhere mentioned in Thomson’s book, in the summer of 1935 the R.C.A.F. attempted a complete aerial survey of Prince Edward Island with overlapping flight lines. This 1935 set is copyright Her Majesty the Queen in Right of Canada, reproduced from the collection of the National Air Photo Library with permission of Natural Resources Canada. The Province has very generously made available to researchers most of the complete aerial surveys of the Island ever done and you can find them here. You are allowed to download for study, in a highly magnified state, every photo in the collection.

The 1935 aerial survey was not perfect, however. The navigator may have been dozing when he guided the plane in lines from North Cape down to Alberton. The result, as shown in a screen capture of the complete Island set by the UPEI geolab webmap viewer shows the big gap, with tiny ones here and there in other areas.


As a side remark, and something about which I know virtually nothing, although this system is used by several of my friends in their Island work, in Wikipedia we find that “A geographic information system (GIS) is a conceptualized framework that provides the ability to capture and analyse spatial and geographic data. GIS applications (or GIS apps) are computer-based tools that allow the user to create interactive queries (user-created searches), store and edit spatial and non-spatial data, analyze spatial information output, and visually share the results of these operations by presenting them as maps.”

So, the 1935 survey is not perfect, and it hurts that the great oversight is in my home territory. Nevertheless, nearly everything in which I have a strong interest is visible. Take for example the Black Marsh at North Cape. I rhapsodised over it in my very first post on The Spirit of the Place. Do you recall this haunting image of a storm brewing, seen through the thorns of the dead Hawbush?

At the end of the ice age around 12,000 years ago, the retreating ice gouged a huge hole in the weaker substrate at North Cape which produced a pond contained by very high hard sandstone cliffs to the northwest. In time this filled with vegetable matter and became a bog filled with sphagnum moss and exotic insect-eating plants like the pitcher plant and the sundew. Settlement was not possible in this floating bog but the Irish settlers who came in the early Nineteenth Century settled around the edge and fished along the beaches of the precipitous cliffs. North Cape itself became a point of intense focus because of the extremely dangerous reef that curved out to sea for several miles. By the 1860s the present magnificent lighthouse had been built to help mariners avoid this danger. Legends of shipwrecks, ghosts and buried treasure abounded and are still remembered by the local residents.

1935 Flight line A-5312-29 – Crown Copyright.

Here in this complete photo, you can see the reef at the bottom, the turbulent patterns of the conflicting sea currents where the Gulf of St. Lawrence divides to form Northumberland Strait, the settled area where the lighthouse is located and behind all this, the great bog known as the Black Marsh. It was also known as, and identified as such in maps, the Hawbush because of a large grove of hawthorn bushes that invaded the edges of the bog. At the very top you can see what looks like a line of big teeth coming out of the shore matrix. These are the great high cliffs, carved in that toothy shape by the violent seas. In time some would separate and become what geologists call stacks. Elephant Rock, North Cape’s greatest tourist attraction ever before the sea dissolved it, was one of these stacks.

Look at the strata in those rocks, built up over millions of years.


Of great interest to me because of its natural history, folklore, family connections and the lobster canning industry is that toothy grin of cliffs in the right part of the photo.

In the early Twentieth Century to the time of World War II this very remote area of coast was the scene of a vigorous lobster canning industry run by Clarence Morrissey, a man of great vision and energy, ruthless, and in his late years, a member of the Island legislature. This last achievement was commemorated in a wicked folksong by local songwriter Alec Shea. This photograph taken from the sea shows his sprawling establishment, which was approached by the Norway Road, sadly missing from the area not photographed by the R.C.A.F. in 1935.

As you can see the factory was perched on the very edge of the cliff because the bog left no other space. Offshore were rich lobster grounds and the contortions Clarence Morrissey went through to build a seasonal harbour were amazing. Fortunately, his family were keen early photographers, and we have these tiny blurry shots from 1914 showing the perilous descent down to the beach where the boats were moored.

It was all such a spectacular effort to capitalise in a remote and dangerous place on rich, dangerously situated lobster banks.

In my world of Island Heritage, continuity and relationships are everywhere to an overwhelming degree. The 1935 photo that inspired this digression was taken at the time my mother, as a child labourer, was sent to work at Clarence Morrissey’s factory. For all I know she may be one of the people specks visible in that photo. Years later, as a talented boy soprano I came to the attention of Clarence Morrissey’s daughter, Frances Fraser, who had been a nurse during the war and who was a rip-roaring pianist of ragtime and Irish tunes. She was a widow with two children, Kathy and Mickey, and I became a regular visitor at their home in Tignish where father Clarence, like a huge Buddha, sat and oversaw the world as Frances played and I sang. Afterwards the grandchildren and I explored the secret shed where the remains of the equipment and supplies of the factory days was stored in a kind of shrine.

It was at this time that the local folk satirist Alec Shea wrote this song, perhaps the most popular of all his compositions.

‘Twas in the summer of 1931
When a bunch of Tories was working at the Run,
They went on the job like a darn bunch of mules
And the first day they worked Oh they lost all the tools,
Over the wharf in the water.

Morrissey, the foreman, he looked pretty cross,
When somebody asked him if he was the boss,
That he forced them to dive for the tools they had lost,
Over the wharf in the water.

‘Twas something peculiar the people all say
They kept Alec Shea for only a day,
And then they sacked him and sent him away,
From working on the new breakwater.

Still the job is not done yet,
And the same old foreman I knew they would get,
For he was the worse that they had there yet,
Since they’re working on the new breakwater.

The following year of nineteen-thirty-two,
Didn’t Morrissey come back with the same old crew?
And he swore to his God he would see the job through,
Working on the new breakwater.


There are many more stanzas that pick out all of Morrissey’s cronies and heap hilarious insults upon them.

It is this kind of continuity of people and places that drives my exploration – and celebration – of the byways of Island social and topographical history.


Other Aerial Photos from 1935

Charlottetown in 1935

The city of Charlottetown and its surrounding areas are fascinating to study in this photo from one of the flight lines.

1935 Flight line A5063-55 – Crown Copyright

The pictures are not oriented north/south so things may look a bit confusing at first. When you crop and reorientate the city you can see that it has kept its original plan to a remarkable degree when you compare it to an early Nineteenth Century plan.

John Plaw, Plan of Charlottetown, 1810. PARO


Looking at this late 1920s oblique photo of the city it all springs to life and life goes on in a busy fashion, all beginning at Queen’s Square and moving to the extremities.

Photo, crica 1928, from the internet.

What a simple, tidy, classical place it all was at that time, the very image of what the Eighteenth-Century planners had prescribed, with orderly expansion into the Royalties.


The 1935 Aerial Photos and Prehistory

There was a considerable degree of activity in Saint Peter’s Bay in remote prehistoric times, as far back as 12,000 years. When you look at the photograph taken of the bay in the Midgell area you can see that it is quite possible that in very remote times it would have been possible to walk across the bay at low tide. Maybe there was no bay in that area, but a land bridge with a drainage outlet for the Saint Peter’s River Pond to the west.

1935 Flight Line 5335-39 – Crown Copyright

One must not forget that, under that bright little cloud that obscures the tip of the Midgell peninsula in this aerial, in 1983 I found these black striated rhyolite artefacts that most likely date from at least 5,000 years ago in the Archaic period. They were all taken to the National Museums in Ottawa and will never again be seen on the Island.


1935 crop marks at the original site of Malpeque?

All human activity on the ground leaves traces that are forever visible in one form or another. They are most easily seen as marks on growing crops where something buried below the ground may affect the growth rate of the plants above. Such a compacted area could be a house foundation, or other solid buried remains of early settlement. Take for example this flight path over the Port Hill/Low Point area in Lot 13. This was the location of intense Acadian activity in the Eighteenth Century before 1758. It is the area that we believe was the first location of Malpeque before it moved across the bay in the British Colonial Period. There have been French/Acadian archaeological sites found in this area and one has been partially excavated. You can experience this story in a fine display at the Acadian Museum in Miscouche.

1935 Flight Line A5074-10 – Crown Copyright

Would crop marks appear in this, or other photos from other dates that could direct archaeologists where to dig?

Here is an excavation of a French/Acadian site on the edge of the bay, photographed in September 2011. The story of this exploration is told in the Acadian Museum at Malpeque.

Photo courtesy of the excavator Claude Arsenault – September 2011.



The Original 1799 Site of Tignish

The first Acadian settlers to arrive at Tignish with the intention of making it their home arrived in the fall of 1799. Next to the Tignish Run (harbour entrance), on the west side, was a huge tidal lagoon that provided ample acres to be drained with dykes and aboiteaux to create farmland. The settlement that had evolved in fifty years was documented by the surveyor John Ball in this detail of a manuscript map in the provincial Archives.

To date there has been no study of the 1935 aerial photograph that covers this area to see whether there are any crop marks, the traces of early settlement, that might be investigated.

Detail from 1935 Flight Line A5312-70 – Crown Copyright.


The house cellar of Thomas Poirier’s house is still visible, causing a kink in the road down to the Green (beach). In the landscape, and from the air, traces of the first settlements of Europeans and their descendants are still visible, connecting everything and waiting to speak to us today.

Also in this area are the sites of the first and second churches (1801 and 1826) which are yet to be located and the original cemetery (1800-1860) which is fenced off and occasionally maintained.


The 1935 aerial maps show the Island at its most exposed, where many thousands of acres are laid bare as fields and where the ground has not been deeply disturbed by the hand ploughs drawn by horses. There are so many archaeological hints to be identified and explored by those who know the topography of the past.



The 1938-49 topographic maps

Ordnance Survey maps originated in England when Scotland was minutely surveyed following the Jacobite Rebellion of 1745. The English realised that they did not have any reliable maps of country and so could not plan their defense. The term “ordnance” indicates the military origins of this mapping project. At the instigation of George II, a map was produced that was the forebear of subsequent developments in the century, leading up to the time of the Napoleonic wars. In 1801 the first one-inch-to-the-mile (1:63,360 scale) map was published and in the next 20 years more and more territory was mapped. Special efforts were made to insert place names in their correct location, something that had been vaguely done in earlier maps. In 1835 the British Geological Survey was founded and remained connected to the Ordnance Survey until 1965. Finally, in 1891, the publication of the one inch to the mile series for all of Britain was completed.

Although these maps had as their prime function the basis of military planning, there was a huge demand for an edition, county by county, for portable versions of the maps that ramblers and the new phenomenon of tourists in motor cars could use to explore the countryside. The maps went through many editions and changes in format but the end result, as in this Ordnance Survey 1:63360 seventh series sheet 170 London S.W. published 1959, took on this format.

A detailed view of a portion of this map shows urban and open country features with great clarity, along with the indication of various kinds of roads and icons to indicated buildings and features of importance to the traveller.


The Topographic map comes to the Island

Detail from the Rustico sheet, 1939, showing major tourist destinations.


Perhaps the greatest encouragement to create a topographic map of Prince Edward Island based on the English system of ordnance maps was the 1935 aerial survey of the Island, showing everything, for the most part, in sharp focus. The flight runs overlapped so it was possible to extract very exact transitions from one photo to the next until a mosaic of almost the whole Island was produced. You may recall that there was one tapering narrow strip from Nail Pond to Alberton that missed being photographed in the kind of error that was the bane of the existence of these skilled aerial surveyors.

I was hesitating in embarking on this portion of this post for the simple reason that I did not have direct access to any of the topo sheets that began to be produced in 1938. I found several for sale, in Gallery 18 in Victoria but was unable to buy them.

It was at this critical moment, when everything had come to a stop, that the thoughtful and kind Harry Holman contacted me to encourage me to consider making mention of these maps even though their production dates went to 1947, a bit beyond my cut-off date for this long-term map project. Harry provided me with information that made sense out of the fragmentary details I had collected about these maps in the past few years. Here is the gist of what he told me in an email:

The 1938(?) inch/mile set of maps made by the Army Survey Establishment at a scale of 1:63,360 has over 10 sheets and extends to about the same size as the original Holland map. Moreover, it has every single building (outside of the urban areas) shown as well as a full range of typographic symbols. It was prepared with the aid of the air photos taken by the R.C.A.F. as well as ground surveys. Prince Edward Island was the first province to be completely mapped through what became the National Topographic System (NTS). In the early 1950s the inch/mile scale was converted to a metric 1:50,000 scale and in 1966-67 and [Edition 2] was published. [In 1978 Edition 3 was published from photographs taken in 1976.]

The 1:50 000 scale topographic map accurately shows hills, valleys, lakes, rivers, streams, rapids, portages, trails and wooded areas; major, secondary and side roads, and all human-made features such as buildings, power lines, dams and cut lines.


Based on his collection Harry Holman was able to provide me with this table of all the maps that make up the survey of the Island, providing the map numbers, where possible, and their date of publication. I have added an extra column to record the dimensions because, in future editions, this would become an issue. I have also rearranged the sequence of publication chronologically. Please note that this table is incomplete and that there will be additions and corrections as time goes by.


Name Number Dimensions Date of Survey Date of Publication
Rustico 11 1/6 18 3/8 x 24 7/8 in 1938 1939
Charlottetown 11 1/3 1938 1939
Summerside 11L5 & 2 1/8 1943 1944
Orwell 11 1/2 West 22 7/8 x 13 1/8 in 1945 1946
Montague 11 1/2 East 1945 1946
Mount Stewart 11 1/7 1945 1946
O’Leary 21 IG 1945 1947
Souris 11 L8 18 ¼ x 25 in 1945 1947
Tignish 21 1/16 22 ½ x 20 in 1945 1947
Malpeque 1945? 1947?
Cape Tormentine 1945? 1947?


Prince Edward Island was the first province in Canada to be mapped in what would become the National Topographic System. The maps were surveyed and produced by the Department of National Defense based on photographs taken by the Royal Canadian Air Force. Since this survey was intended in time to cover the entire country, decisions had to be made on the scale to be used and what the size and orientation of the individual maps would be. The locator map that appeared in the margin of each published Island topographic map not only showed the progress of the project – tinted green – but also the shape of the maps based on one inch to one mile. In all there were 11 rectangular shapes, vertical and horizontal, in roughly four different sizes.

It is interesting to speculate on the order in which the various maps were published. The first two maps to be published on the eve of World War II were at the peak of the post-Depression surge in tourism which had been building with a new intensity since the introduction of the motor car in the 1920s. Obviously the maps of Rustico and Charlottetown are directed at the tourism industry. The Rustico map contains the heart of what is still our tourism mecca and Charlottetown, of course, contains the capital with all its urban delights. And then the war started. Why would the series continue in wartime with the Summerside map? It was the airport, of course, and its subsidiary runways and hangars at Mount Pleasant.


Wartime postcard of Summerside with the airport site vaguely indicated.


At the moment, my only source of images of several maps displayed in their entirety come from the Gallery 18 site of maps the shop has for sale and which are available online. I express my gratitude to Aubrey Bell for providing these images.

Here is the Gallery 18 photo of the 1939 printing of the Rustico area. The size of the map is 18 3/8 x 24 7/8″.


1939 Rustico

This is probably the first map that appeared in Series 1 and it and its companion map of Charlottetown, that appeared at the same time, probably set the design standards for all subsequent maps of the Island. It is a handsome format with all credits given and a locator map provided so you could see the mapping pattern for the whole region.


1947 Tignish

Another image of a complete map I can include at this time is the one for Tignish. It is interesting to see that it includes North Cape while in the earlier locator map of the period the latitude grid cuts it off. In the next 2 series it will be cut off and a whole mostly empty topo sheet had to be bought for that small area.


Gallery 18 posted a detail of the North Cape area from the Tignish map they have for sale. I find it deeply interesting for two reasons. First it accurately maps the Black Marsh as it existed at that time, and also the location of the lighthouse and its associated buildings. The lighthouse would be moved back from the rapidly eroding cliffs three times in my lifetime! Secondly it permits me to retrace my footsteps as, just a boy, I explored all around North Cape and even the site of Clarence Morrissey’s fish factory on the very narrow strip of usable land between the Marsh and the cliffs eroding erratically into a toothy pattern.

Detail of North Cape from the Tignish Topo map- Gallery 18 Collection.

Harry Holman, knowing my propensity always to start my examination of a map in Lot 1, thoughtfully provided me with scans of the Tignish area, the place where I spent the first 14 years of my life.

Detail of Tignish from the Tignish Topo Map from the Harry Holman Collection.

Looking at the Tignish area from that time I was amazed to see the dot that represented my grandparent’s house in a field at the very end of the Western Road. That is the only visual record of out few years spent in that spot before the house was moved to another location. It does not appear on either the 1935 or 1958 maps, not even in its new location. And looking west beyond that, where the forest began, clearly marked was the very spring and brook where my interest in Fresh Water biology began as I collected specimens to look at under the toy microscope I had received for Christmas.


1946 Orwell

Gallery 18 also has a view of the Orwell map, which has an unusual tall vertical shape, as the does the Montague map next to it.

Desperate to fit the eccentric Island into a formal regular grid, the mapmakers gave up and simply increased the length of those two maps. Also desperate, and in a very old cartographic tradition, Point Prime juts out into the margin.

Again, thinking of my geographic attachments, Harry Holman sent me scans of the area in this map that contains Belle River in Lot 62.

Clearly marked was the small property on which I have lived for the past 21 years, and very importantly, for the first time, I had a document that showed the configuration of the harbour in the days when there was mooring for schooners and many fish factory buildings that belonged, in the end, to the Riley family, the local magnates. This is the Belle River wharf as it was when the first aerial survey was made and when the first series of topographical maps was printed.

And this was the busy wharf at the same time.

Photo courtesy Shirley Krug.

Gradually this long period of prosperity, illustrated in the aerial photos and topo maps, came to and end, and decay set in.

Today, when you walk out at low tide at the mouth of the Belle River, this is the site of everything you saw in the preceding photographs. Its all gone, collapsed, and rotted away.

If the tide is very low you will see these beautiful quartzite glacio-fluvial cobbles – millions of them, 12,000 years old – littered here and there with broken bricks, rotting wharf piles, and bits of metal, all that remains of that season in that place.

 To every thing there is a season, and a time to every purpose under the heaven:

 A time to be born, and a time to die; a time to plant, and a time to pluck up that which is planted;

 A time to kill, and a time to heal; a time to break down, and a time to build up;

 A time to weep, and a time to laugh; a time to mourn, and a time to dance;

 A time to cast away stones, and a time to gather stones together; a time to embrace, and a time to refrain from embracing;

 A time to get, and a time to lose; a time to keep, and a time to cast away;

 A time to rend, and a time to sew; a time to keep silence, and a time to speak;

 A time to love, and a time to hate; a time of war, and a time of peace.

Ecclesiasticus 3, 1-8




One of the first maps I presented to you a year and a half ago was a Mediaeval mappamundi that shows how the world was seen at that time, with Adam and Eve and Jerusalem at the top, next to the heavenly realm, and spreading below is the rest of the world, seen as if in a great bird’s eye view. This kind of map represents the beginning of trying to represent the world intelligibly on parchment. The times required that God be present to overview His creation.

This satellite map of Prince Edward Island is also a view from heaven, but a view that illustrates in the most spectacular fashion my thesis that the Island is a human artefact. Everywhere you look you can see lines and mases in the landscape from one end of the Island to the other that are there because of Samuel Holland’s survey. Those lines, based on the Magnetic North of 1764 account for almost everything we see in the topography and landscape of the Island.

This satellite view also is the culmination of centuries of attempts to depict the world in a meaningful way. The eye of God has been replaced by the lenses and sensors of satellites circling the earth in search of a multiplicity of data that will lead to yet more insights from the traditionally highest concept of all – Heaven.

Satellite map from the internet.



Special Thanks

I am very grateful to Harry Holman and the interest he showed in this particular post. Not only did he help me along with a summary of the emergence of topographical maps on the Island but he also sent me some very clear scans from some of the maps in his personal collection.

I am also grateful to Aubrey Bell of Gallery 18 for posting photos of topographical maps he has for sale and which I greedily inserted as illustrations in this post.



Bradford, John, Ancient Landscapes: Studies in Field Archaeology, G. Bell and Sons, Ltd., London, 1957.

Deuel, Leo, Flights into Yesterday: The Story of Aerial Archaeology, Penguin Books, Harmondsworth, Middlesex, 1969.

Thomson, Don W., Skyview Canada: A Story of Aerial Photography in Canada, Energy, Mines and Resources Canada, Ottawa, 1975.

Werle, Dirk, “Historical Air Photo Missions in the Maritimes during the Early 1920s: Coverage, Thematic Scope, And Utility 100 Years Later,” Proceedings of The Nova Scotian Institute of Science, Volume 51 Part 1, pp. 145-167, 2021.