• In 1599, Sems became a
silk merchant in
Leeuwarden. • 1600: The book
Practijck des lantmetens, a book written by Sems and
Jan Pietersz. Dou, was published. The book was used at the engineering school started by
Simon Stevin. • 1602: Sems was appointed
land surveyor of
Friesland. • 1603: Sems made a detailed map of
Leeuwarden, which was engraved by
Pieter Bast. • 1604-1608: Sems had the supervision over the building of the fortifications at
Bourtange,
Delfzijl and
Bellingwolde. • Sems bought several buildings in the city center of
Leeuwarden. • Around 1610, Sems moved to
Bunde in
Germany and he bought land in the
Bunder Neuland, a
polder that was created in 1604, with help from investors mainly from
Amsterdam. • 1615: Sems and
Johan de la Haye determined the exact location of the border between
Groningen and
Drenthe, the
Semslinie. They took the
Martini tower as a reference point, but later measurements have shown that it would miss the
Martini tower by 532 meters. • 1616: From April 30, Sems was involved in
land reclamation at
Bredstedt. Later that year he designed the
Christianshavn on
Amager. • 1618: On January 6, while he was in
Denmark, Sems was asked to come to the Netherlands because of a border dispute between
Groningen and
Drenthe. at
Ter Apel. • 1621: Sems was back in Bunder Neuland. There were disputes between the
Staten Generaal and
Enno III, Count of East Frisia, about who had the rights in the
polder. • ca 1623: Sems was appointed
dijkgraaf in the Bunder Neuland. In 1623,
Jacob Matham produced an engraving of him, based on a portrait by Martin Faber. • 1623: Sems lived in
Groningen and his book
De arithmetische fundamenten was published in
Emden. • 1625: The polder at
Bredstedt was swept away by the sea during a storm. • 1626: Sems was given the task to map the area north of
Pieterburen. • 1628: Sems got involved with the fortifications in eastern
Groningen again. • 1629 en 1632: Sems's 'movable possessions' (excluding real estate) were seized due to default of payment. • 1634: Sems was in
Dutch Brazil where he was involved as an engineer in the construction of fortifications at the conquered cities. Sems was married twice: first to Baerthe van Soutelande and then to Catharina Jans. ==Death==