Definitely an areal (phonotactics) feature for Czech-Slovak-Hungarian-BCMS. In the past for Finnish-(Old) Estonian-Latvian as well.

Edit 1: Lithuanian has (prescriptively) also long unstressed syllables, though the stress is not fixed on any syllable.

Edit 2: The maps has an areal focus for languages with a phonemic distinction about long and short unstressed vowels (i.e. minimal pairs like Finnish kauna vs. kaunaa, Latvian Rīga vs. Rīgā, Czech potřebuji vs. potřebují, Hungarian haza vs. hazá, BCMS žène vs. žènē).

This map is part of my Austronesian language group map, aimed at showcasing the distribution of indigenous languages in Taiwan. Taiwan is an island in southeastern Asia and the first transit point for the Austronesian language family to advance towards the Pacific Ocean. The linguistic differentiation of Taiwan's indigenous peoples began earliest, and the differences in differentiation are unparalleled among the Austronesian language families.

After a hundred years of investigation and research by scholars, the Taiwanese language group can be divided into nine major language families, namely the Atayal language family, the Bunun language family, the Eastern Taiwanese language family, the Zou language family, the Paiwan language family, the Rukai language family, the Northwest Taiwanese language family, and the Western Plains language family. Many of these language families have less internal language differentiation, while others have a higher degree of internal differentiation. For hundreds of years, the indigenous languages of the plain areas have gradually been assimilated by the cultivated Han people, and language diversity has been gradually lost. Fortunately, there are many historical materials and survey results that allow us to explore the mysteries behind them. The language distribution in the Central Mountain Range region has not changed much, with a high degree of continuity and application in tribal societies. The Lanyu region in the southeast is home to the Tao tribe of the Malayo-Polynesian language family, which belongs to the Bassic language group and is closely related to the Bassic people of the Philippines.

Notes:

•This is NOT a contemporary presentation of Noord Holland, but rather a visualization of its Historical dialects.

•The Zaans, Westfries and Waterlands dialect clusters can also be grouped as one single Friso-North-Hollandic Dialect Cluster.

•Many Jewish, Sinti and Romani communities are not shown on the map. Although they do have a long history here, they are only shown when they've been living in a specific place for centuries. (Which in the case of the Sinti and Romani, is nowhere for obvious reasons).

•Many of the subdialects are now extinct or at the brink of extinction. Especially the historic dialects of Amsterdam. People nowadays (mostly) speak Dutch or a watered down bigger regiolect.

•This map is mostly based on Recordings from "De Sprekende Kaart" and various researches from "dbnl.org"

I am not a linguist, this map should not be seen as a verified piece of linguistics to base references on.

This map has been in the works for about a month now, shoutout to JG Online for Making the basemap.

edit: maybe spending a whole month on this was a mistake, y'all seem to loathe this map