2.1 Guillaume De L’Isle (1675 - 1726)

French cartographer who studied under the guidance of the astronomer Jean-Dominique Cassini, he was admitted into the French Academy of Sciences in 1702. In 1718, he gained a full membership of this institution and was appointed Chief Royal Geographer, so he had access to news of the latest discoveries and issued several maps particularly of France’s colonial possessions in America.

During 1703 he published a map of the northern part of South America, it renders the region in extraordinary detail offering both topographical and political information with forest and mountains beautifully rendered in profile. This, like most early maps, contrasts a detailed mapping of the coast with a speculative discussion of the interior, particularly the Amazon basin. He credits the mappings and explorations for Antonio de Herrera, Joannes de Laet, Cristobal de Acuña and Manuel Rodríguez (^{Daniel Crouch Rare Books, 2021}).

2.2 Samuel Fritz (1654 - 1725 or 1730)

Czech Jesuit missionary who entered the Society of Jesus in 1673 where he probably studied cartography, then in 1683 he decided to go as a missionary to South America. He began his career in 1686 and was assigned the task of incorporating the territory between Napo River and Río Negro, that territory spanned about 700 kilometers along the Amazon River and was inhabited by the Omagua nation. In the late 1680s, the Maynas mission had probably included the Omagua Indians, and their neighbors the Yurimagua, Aisure, and Ibanoma because the work done by him.

In 1707, he engraved his map with the help of the Jesuit Juan de Narvaez whose initials appear on the title, and the support of the colonial authorities of Quito so it was dedicated to Phillip V, King of Spain. This map shows the course of the Amazon River from its headwaters close to Quito to its mouth at the Atlantic Ocean, a high level of detail of the hydrography in the region is shown, as well as the names of the towns and the tribes that inhabit them (^{Dias, 2012}).

2.3 Charles Marie de La Condamine (1701 - 1774)

French mathematician and naturalist who achieved the first scientific exploration of the Amazon River. In 1735, he participated in an expedition to determine the longitude of a degree of meridian near the equator led by the mathematician Louis Goudin until 1743. After, La Condamine decided to change the way back to Europe taking the Amazon River course as a route to reach the Atlantic Ocean, his primary motivation was to produce a map “of the course of a river that traverses vast lands nearly unknown to [French] geographers” (La Condamine, 1747).

Finally, the presentation of the results was in 1745 including a map based on his observations. La Condamine was the person that took the measurements and the French geographer Jean-Baptiste Bourguignon d’Anville was the responsible to draw it (^{Cintra, 2011}). The map includes the Pacific and Atlantic coast, it extended from the Spanish province of Quito in the west to the Portuguese city of Grão Pará (Belém) in the east, including the Guyanas to the north and parts of Brazil and Peru to the south.

2.4 Emanuel Bowen (1694 - 1767)

English engraver, publisher, and map seller in London from 1720 to 1767. His remarkable work earned him the rare distinction of being Royal Mapmaker to both, King George II of Great Britain, and Louis XV of France. He was highly regarded by his colleagues for producing some of the largest, detailed, and accurate maps of his era, due to his reputation he worked with most of the British cartographic figures of the period including John Ow’en and Herman Moll.

The maps that belong to his world atlas The Complete System of Geography’ have a distinctive and attractive style, rococo cartouches with vignettes representative of the areas shown, and annotations describing the region. This work is a description of countries, islands, cities, ports, lakes, rivers, mountains, and mines of the known world published in two volumes, it contains seventy maps that were drawn and engraved according to the latest discoveries and surveys of the time; one of which includes the representation of the Amazon River and its tributaries.

2.5 Károly Brentán (1694 - 1752)

Hungarian Jesuit missionary that spent a long time in South America, mainly performing tasks of evangelization and education with the indigenous population in the territories that are now Colombia, Ecuador, and Peru. The Marañón River was the area where he carried out his religious activities, he lived in the Andoa tribe but later visited the Miguiano, Amaono and Parano tribes (^{Lazca, 2000}).

In 1747, his superiors sent him to Rome to represent the province of Quito. One year later, together with the Spanish missionary Nicolás de la Torre, they left Quito and traveled to the city of Grão Pará (Belém), taking the river route along the Amazon River. All his notes disappeared after his death, only a map intended as an appendix remained. Giovanni Petroschi, who had been close to the Jesuit order and had published several maps of South America, published the map, the Roman Cigni brothers were in charge of drawing and engraving. One copy can be found in the British Museum and in the Ecuadorian Library Aurelio Espinosa Pólit (^{Korányi, 2017}).

3.1 Calculation of the scale

Using CorelDRAW, the images were resized based on the data obtained from consultations with online libraries that have an original or a copy of the maps in their collection (Table 2). Then, the distance between two consecutive parallels was calculated in order to establish the measurement of a degree of latitude and to compare this with the real distance on the ground. In order not to depend on a single measurement, between four or six measurements were made to have a greater sample of data and determine a more accurate result (Table 3, 4, 5, 6, 7). Scales are expressed by its denominator.

The origin of the measurements is the equatorial line, for which positive positions are calculated for northern latitudes and negative positions for southern latitudes. For a better visualization of the process, a screenshot of the map A_GI and the position of the parallels taken as a reference are included (Figure 1).

Figure 1 Position of the parallels of A_GI. 

With the estimated data, an average scale can be determined for each map and its corresponding standard deviation, which indicates the margin of error of the process (Table 8). This method is based on the dimensions described in table 2, if the values change depending on the source, the calculation must be carried out again.

3.2 Calculation of the meridian of origin

In Global Mapper, images were georeferenced using the meridian and parallel intersections as control points in the drawn grid of each map. The georeferenced images were imported to QGIS Desktop, in which the longitude of 15 or 20 locations were determined in the coordinate system of each map, depending on the case; after from these same locations its current longitude was determined taking Greenwich as the meridian of origin. Finally, in a calculation table the Equation 1 was applied with the collected data, thus calculating the meridian of origin in reference to each of the locations (Table 9, 10 y 11).

λorig: Longitude of the meridian of origin in relation to Greenwich.

λG: Longitude of the point relative to Greenwich, obtained from a current map.

λa: Longitude of the measurement point on the map.

For a better visualization of the process, a screenshot of the georeferenced map A_GI and the distribution of the locations taken as a reference for the calculation of the meridian of origin is included (Figure 2).

Figure 2 Distribution of the locations of A_GI. 

It should be added that the name of the locations was taken from each map, so there may be spelling mistakes or not coincidence with which it currently has. With the calculated data, an average λorig can be determined for each map and its corresponding standard deviation, which indicates the margin of error of the process (Table 12). In relation to the C_LC and D_EB maps, it was not necessary to carry out the previous procedure since each author described the meridian of origin used in their work.

3.3 Determination of the map projection

Using CorelDRAW, the grid drawn on each map was delineated for a better visualization of its shape and the angles formed between meridians and parallels. Then, the distances between each of the meridians and parallels were calculated, taking the left and upper sides of the map as a reference (Table 13, 14, 15). The origin of the measurements for the parallels is the equatorial line, for which positive positions are calculated for northern latitudes and negative positions for southern latitudes; in the case of meridians, the origin of the measurements is a random meridian from which the positions to its left are negative and to its right are positive. For a better visualization of the process, a screenshot of how A_GI map grid looks like is included (Figure 3).

Figure 3 Drawn grid of A_GI. 

With the drawn grid, the type of line with which the meridians and parallels were represented and the distance between each of them, the most probable map projection used was determined (Table 16). In relation to the C_LC and E_KB maps, it was not possible to carry out the previous procedure since each author did not depict any grid in their work.

3.4 Process of georeferencing and digitalization of the main features

The data determined in the previous process allowed to perform a correct georeferencing of the images using Global Mapper (Table 17). An adjustment was made with 4 control points for each of the maps, with the exception of the B_SF in which 6 control points were used. Once each one of the georeferencing process was finished and its correct execution was verified, the images were exported to GeoTIFF (.tif) format together with their corresponding PRJ file (.prj).

With the georeferenced images, the digitalization of the main features such as cities, rivers and coastlines began using the QGIS Desktop.¹¹ Later, the Project Coordinate Reference System (CRS) was defined based on the parameters described in Table 17 and a GeoPackage (.gpkg) file was created to store the digitalized shapefiles.

The necessary shapefiles were created to represent the cities, rivers, and coastlines, setting the geometry type (point, line, or polygon) and the fields of the attribute table (name and level). Then, the digitization process was carried out, in the case of the cities and rivers, these elements were classified according to the symbology represented by each author in the original map, establishing categories in reference to their importance and flow, respectively. Finally, the attribute table was loaded with the map information and a particular style was defined for each shapefile that allows a quick identification of the entity it represents (Figure 4). Once the digitalization process was finished, the shapefiles were exported to GeoJSON (.geojson) format.

Figure 4 A_GI digitalized map. 

3.5 Comparison of the maps

The process of comparing the maps was carried out using MapAnalyst, each image was imported and defining its resolution (dpi). Later, each one of the control points between the old map and OpenStreetMap¹⁴ was determined and a name was assigned that allows its identification. In relation to the control points, common locations were selected among the five maps in order to better visualize and interpret the results, these sites were easily identifiable cities and main river mouths that in few exceptions were not represented (Table 18).

Once the control points were correctly determined and distributed, the compute option was selected, generating the graphical visualization of the comparison. The selected method was Displacements showing the variation of the position using Vectors & Circles at a scale factor of 1 (Figure 5). When each one of the comparison processes was finished, the images were exported to JPEG (.jpg) format.

Figure 5 Process of comparison of A_GI using MapAnalyst. 

4.1 A_GI map

Visibly there was a greater knowledge of the cities in Ecuador and Peru, while in the Amazon and the Brazilian coast there is a reduced number of these. The coastal profile on the Brazilian coast is not detailed, the islands at the river mouth do not match with reality and were represented by several fragmented islands.

Regarding the positional displacements, it can be observed that they exist to a greater extent in the area of Ecuador and Peru, being the location of S. Francois de Borgia (Borja) an outlier of the control points. This great difference that can be observed in the terms of positional displacement is because the author took different sources of consultation to carry out his work (in the map title the author described the names of the sources) (Figure 6).

Source: National Library of Brazil.

Figure 6 A_GI compared map. 

4.2 B_SF map

The map can be divided into two for an analysis starting from the central meridian to the west, in the Spanish territory an important level of detail is displayed, the opposite case occurs from the central meridian to the east (Portuguese territory). A greater knowledge of the cities in Ecuador and Peru is maintained, besides the first towns appear in the Amazon. The coastal profile has little accuracy with reality, the river mouth on the Brazilian coast was represented by countless islands of small and medium size.

The positional displacement shows the lower precision of the control points in Ecuador and Peru (presumably a bad longitudinal positioning), although clearly along the river course it can be presumed that there were adjustments in the determination of the position, that allowed greater precision between the Rio Negro and Paru river until reaching the mouth of the Amazon River (Figure 7).

Source: National Library of France.

Figure 7 B_SF compared map. 

4.3 C_LC map

Being the work of Samuel Fritz earlier, and in order to establish a comparison between it and his map, the author included the Amazon River course and its most important tributaries drawn by Fritz as a background (dotted line). More cities in the Amazon are included. The coastal profile does not match in the part of the Gulf of Guayaquil, being deformed towards the continent, the Isle des Joanes ou de Marayo (Ilha de Marajó) is represented at the river mouth in the Mer du Nord (Atlantic Ocean) surrounded by few small islands.

The positional displacement is variable, in Ecuador and the northern Peru a greater displacement is visualized except for Jaen and Borja compare with the locations near the Brazilian coast, the mouth of the Napo River is the outlier. It can be presumed that in several positions the measurements did not follow the same methodology, or they were not carried out and external data sources were taken as reference (Figure 8).

Source: National Library of France.

Figure 8 C_LC compared map. 

4.4 D_EB map

The map is part of a world atlas prepared by the author. According to his description the sources of consultation were French maps from which he took the information. More cities are included in the eastern part of Ecuador and Peru. In the Amazon and the Brazilian coast, main cities are consolidated, and secondary cities appear. The coastal profile in Ecuador and Peru is irregular, the river mouth in the Atlantic Ocean does not match with reality since it was represented by islands of medium and small extension with a latitudinal displacement of the entire area towards the south.

The positional displacement is variable, on the Ecuadorian and Peruvian coasts it is greater compared to the central zone of both countries, the city of Napo (Tena) and St. Francois d’ Borja (Borja) show the largest displacement while at the Topayos River mouth is the shortest. Finally, on the Brazilian coast a lower positional accuracy is visualized (Figure 9).

Source: National Library of Brazil

Figure 9 D_EB compared map 

4.5 E_KB map

A greater presence of cities is displayed on the Brazilian coast. The coastal profile in Ecuador and Peru is irregular considering that the river mouths towards the sea are wider and penetrate the continent. The Ins. De Joannes alias de Marayo (Ilha de Marajó) surrounded by few small islands was represented at the river mouth in the Mar Septentrio (Atlantic Ocean).

The author belonged to the same religious mission as Samuel Fritz, so it can be assumed that he had access to its reports and maps, therefore it is observed that basic information remains on the map supplemented with the data obtained from his explorations. The positional displacement is greater in Ecuador and Peru compare with the control points along the river course and the Brazilian coast, the Napus (Napo) River mouth is an outlier of the control points. From the Tefe River mouth to the Brazilian coast, the positional precision improves so adjustments may have been made in the determination of the position (Figure 10).

Source: National Library of France

Figure 10 E_KB compared map